Webster's Dictionary, 1913

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Irritancy noun [ From 1st Irritant .] (Scots Law) The state or quality of being null and void; invalidity; forfeiture. Burrill.

Irritancy noun [ From 2d Irritant .] The state or quality of being irritant or irritating.

Irritant adjective [ Late Latin irritants , -antis , present participle of irritare to make null, from Latin irritus void; prefix ir- not + ratus established.] (Scots Law) Rendering null and void; conditionally invalidating.

The states elected Harry, Duke of Anjou, for their king, with this clause irritant ; that, if he did violate any part of his oath, the people should owe him no allegiance.

Irritant adjective [ Latin irritans , -antis , present participle of irritare : confer French irritant . See Irritate to excite.] Irritating; producing irritation or inflammation.

Irritant noun [ Confer French irritant .]

1. That which irritates or excites.

2. (Physiol. & Med.) Any agent by which irritation is produced; as, a chemical irritant ; a mechanical or electrical irritant .

3. (Toxicology) A poison that produces inflammation.

Counter irritant . See under Counter . -- Pure irritant (Toxicology) , a poison that produces inflammation without any corrosive action upon the tissues.

Irritate transitive verb [ See 1 st Irritant .] To render null and void. [ R.] Abp. Bramhall.

Irritate transitive verb [ imperfect & past participle Irritated ; present participle & verbal noun Irritating .] [ Latin irritatus , past participle of irritare . Of doubtful origin.]

1. To increase the action or violence of; to heighten excitement in; to intensify; to stimulate.

Cold maketh the spirits vigorous and irritateth them.

2. To excite anger or displeasure in; to provoke; to tease; to exasperate; to annoy; to vex; as, the insolence of a tyrant irritates his subjects.

Dismiss the man, nor irritate the god:
Prevent the rage of him who reigns above.

3. (Physiol.) To produce irritation in; to stimulate; to cause to contract. See Irritation , noun , 2.

4. (Medicine) To make morbidly excitable, or oversensitive; to fret; as, the skin is irritated by friction; to irritate a wound by a coarse bandage.

Syn. -- To fret; inflame; excite; provoke; tease; vex; exasperate; anger; incense; enrage. -- To Irritate , Provoke , Exasperate . These words express different stages of excited or angry feeling. Irritate denotes an excitement of quick and slightly angry feeling which is only momentary; as, irritated by a hasty remark. To provoke implies the awakening of some open expression of decided anger; as, a provoking insult. Exasperate denotes a provoking of anger at something unendurable. Whatever comes across our feelings irritates ; whatever excites anger provokes ; whatever raises anger to a high point exasperates . "Susceptible and nervous people are most easily irritated ; proud people are quickly provoked ; hot and fiery people are soonest exasperated ." Crabb.

Irritate adjective Excited; heightened. [ Obsolete]

Irritation noun [ Latin irritatio : confer French irritation .]

1. The act of irritating, or exciting, or the state of being irritated; excitement; stimulation, usually of an undue and uncomfortable kind; especially, excitement of anger or passion; provocation; annoyance; anger.

The whole body of the arts and sciences composes one vast machinery for the irritation and development of the human intellect.
De Quincey.

2. (Physiol.) The act of exciting, or the condition of being excited to action, by stimulation; -- as, the condition of an organ of sense, when its nerve is affected by some external body; esp., the act of exciting muscle fibers to contraction, by artificial stimulation; as, the irritation of a motor nerve by electricity; also, the condition of a muscle and nerve, under such stimulation.

3. (Medicine) A condition of morbid excitability or oversensitiveness of an organ or part of the body; a state in which the application of ordinary stimuli produces pain or excessive or vitiated action.

Irritative adjective
1. Serving to excite or irritate; irritating; as, an irritative agent.

2. Accompanied with, or produced by, increased action or irritation; as, an irritative fever. E. Darwin.

Irritatory adjective Exciting; producing irritation; irritating. [ R.] Hales.

Irrorate transitive verb [ imperfect & past participle Irrorated ; present participle & verbal noun Irrorating .] [ Latin irroratus , past participle of irrorare to bedew; prefix ir- in + ros , roris , dew.] To sprinkle or moisten with dew; to bedew. [ Obsolete]

Irrorate adjective (Zoology) Covered with minute grains, appearing like fine sand.

Irroration noun [ Confer French irroration .] The act of bedewing; the state of being moistened with dew. [ Obsolete] Chambers.

Irrotational adjective (Physics) Not rotatory; passing from one point to another by a movement other than rotation; -- said of the movement of parts of a liquid or yielding mass. Sir W. Thomson.

Irrubrical adjective Contrary to the rubric; not rubrical.

Irrugate transitive verb [ Latin irrugatus , past participle of irrugare to wrinkle.] To wrinkle. [ Obsolete]

Irrupted adjective [ Latin irruptus , past participle of irrumpere to break in; prefix ir- in + rumpere to break or burst. See Rupture .] Broken with violence.

Irruption noun [ Latin irruptio : confer French irruption . See Irrupted .]

1. A bursting in; a sudden, violent rushing into a place; as, irruptions of the sea.

Lest evil tidings, with too rude irruption
Hitting thy aged ear, should pierce too deep.

2. A sudden and violent inroad, or entrance of invaders; as, the irruptions of the Goths into Italy. Addison.

Syn. -- Invasion; incursion; inroad. See Invasion .

Irruptive adjective Rushing in or upon.

Irvingite noun (Eccl.) The common designation of one a sect founded by the Rev. Edward Irving (about 1830), who call themselves the Catholic Apostolic Church. They are highly ritualistic in worship, have an elaborate hierarchy of apostles, prophets, etc., and look for the speedy coming of Christ.

Is intransitive verb [ Anglo-Saxon is ; akin to G. & Goth. ist , Latin est , Greek ..., Sanskrit asti . √9. Confer Am , Entity , Essence , Absent .] The third person singular of the substantive verb be , in the indicative mood, present tense; as, he is ; he is a man. See Be .

» In some varieties of the Northern dialect of Old English, is was used for all persons of the singular.

For thy is I come, and eke Alain.

Aye is thou merry.

» The idiom of using the present for future events sure to happen is a relic of Old English in which the present and future had the same form; as, this year Christmas is on Friday.

To-morrow is the new moon.
1 Sam. xx. 5.

Is- See Iso- .

Isabel noun , Is"a*bel col"or [ French isabelle .] See Isabella .

Isabella noun , Is`a*bel"la col"or [ Said to be named from the Spanish princess Isabella , daughter of king Philip II., in allusion to the color assumed by her shift, which she wore without change from 1601 to 1604, in consequence of a vow made by her.] A brownish yellow color.

Isabella grape (Botany) A favorite sweet American grape of a purple color. See Fox grape , under Fox.

Isabella moth (?; 115). (Zoology) A common American moth ( Pyrrharctia isabella ), of an isabella color. The larva, called woolly bear and hedgehog caterpillar , is densely covered with hairs, which are black at each end of the body, and red in the middle part.

Isabelline adjective Of an isabel or isabella color.

Isagelous (īs*ăg"ĕ*lŭs) adjective [ Is- + Greek a`gelos information.] Containing the same information; as, isagelous sentences. "The coded message and the original, though appearing entirely unlike, are completely isagelous ." Bacon "The complementary strands have isagelous sequences." J. D. Watson. -- Is"a*gel noun One of two or more objects containing the same information.

Isagoge noun [ Latin , from Fr. ..., from ... to introduce; ... into + ... to lead.] An introduction. [ Obsolete] Harris.

Isagogic, Isagogical adjective [ Latin isagogicus , Greek ....] Introductory; especially, introductory to the study of theology.

Isagogics noun (Theol.) That part of theological science directly preliminary to actual exegesis, or interpretation of the Scriptures.

Isagon (ī"sȧ*gŏn) noun [ Greek 'i`sos equal + gwni`a angle: confer French isagone , adjective ] (Math.) A figure or polygon whose angles are equal.

Isapostolic adjective [ Greek ....] Having equal, or almost equal, authority with the apostles of their teachings.

Isatic, Isatinic adjective (Chemistry) Pertaining to, or derived from, isatin; as, isatic acid, which is also called trioxindol .

Isatide noun (Chemistry) A white crystalline substance obtained by the partial reduction of isatin. [ Written also isatyde .]

Isatin noun [ See Isatis .] (Chemistry) An orange-red crystalline substance, C 8 H 5 NO 2 , obtained by the oxidation of indigo blue. It is also produced from certain derivatives of benzoic acid, and is one important source of artificial indigo. [ Written also, less properly, isatine .]

Isatis noun [ Latin , a kind of plant, Greek ... woad.] (Botany) A genus of herbs, some species of which, especially the Isatis tinctoria , yield a blue dye similar to indigo; woad.

Isatogen noun [ Isat in + -gen .] (Chemistry) A complex nitrogenous radical, C 8 H 4 NO 2 , regarded as the essential residue of a series of compounds, related to isatin, which easily pass by reduction to indigo blue. -- I*sat`o*gen"ic adjective

Isatropic adjective [ Is- + atrop ine.] (Chemistry) Pertaining to, or designating, an acid obtained from atropine, and isomeric with cinnamic acid.

Ischiac (ĭs"kĭ*ăk) adjective (Anat.) See Ischial .

Ischiadic (ĭs`kĭ*ăd"ĭk) adjective [ Latin ischiadicus , Greek 'ischiadoko`s , from 'ischi`on the hip joint, hip or loin. Confer Sciatic .] (Anat.) Ischial. [ R.]

Ischiadic passion or disease (Medicine) , a rheumatic or neuralgic affection of some part about the hip joint; -- called also sciatica .

Ischial (ĭs"kĭ* a l) adjective (Anat.) Of or pertaining to the ischium or hip; ischiac; ischiadic; ischiatic.

Ischial callosity (Zoology) , one of the patches of thickened, hairless, and often bright-colored skin, on the buttocks of many apes, as the drill.

Ischiatic (ĭs`kĭ*ăd"ĭk) adjective (Anat.) Same as Ischial .

Ischiocapsular (?; 135) adjective [ Ischium + capsular .] (Anat.) Of or pertaining to the ischium and the capsule of the hip joint; as, the ischiocapsular ligament.

Ischiocerite noun [ Greek 'ischi`on the hip + ke`ras a horn.] (Zoology) The third joint or the antennæ of the Crustacea.

Ischion Is"chi*um noun [ Latin , Greek 'ischi`on .]
1. (Anat.) The ventral and posterior of the three principal bones composing either half of the pelvis; seat bone; the huckle bone.

2. (Zoology) One of the pleuræ of insects.

Ischiopodite noun [ Greek 'ischi`on the hip joint + ..., ..., foot.] (Zoology) The third joint of the typical appendages of Crustacea.

Ischiorectal adjective [ Ischium + rectal .] (Anat.) Of or pertaining to the region between the rectum and ishial tuberosity.

Ischuretic adjective Having the quality of relieving ischury. -- noun An ischuretic medicine.

Ischury noun [ Latin ischuria , Greek ...; ... to hold, check + ... urine: confer French ischurie .] (Medicine) A retention or suppression of urine.