1) Isotonic 
<physiology> Having the same total osmotic pressure or osmolality as another fluid (ordinarily intracellular fluid); such a fluid is not isosmotic if it includes solutes that freely permeate cell membranes. ... Synonym: iso-osmotic. ... (05 Mar 2000) ... 
(i″soz-mot´ik) having the same osmotic pressure.
Type: Term Pronunciation: ī′sos-mot′ik Definitions: 1. Having the same total osmotic pressure or osmolality as another fluid (ordinarily intracellular fluid); such a fluid is not isotonic if it includes solutes that freely permeate cell membranes. Synonyms: isoosmotic
isotonic (def. 1).