1) French word used in English 2) Legal terminology 1) Stater 
A declarant, generally speaking, is anyone who composes and signs a statement or declaration alleging that the information he has given therein is true. This differs from an affiant, as in the case of an affidavit the facts therein are sworn to before a notary public or other official, whereas a declaration is usually made by one person for the us...
• (n.) One who declares.
The person legally responsible for the accuracy of the information given in a declaration to customs. This includes the accuracy of any supporting documents relating to the declaration.
a person who signs a written statement of facts true to his knowledge. Lying intentionally amounts to offence of making false statements under oath.
De·clar'ant noun [ Confer French déclarant , present participle of déclarer .] (Law) One who declares. Abbott. 
Person who makes a statement. 28 USC. (2) The person who makes a living will. Several states' laws refer to "declarations" in describing living wills or durable powers of attorney, and consequently the statutes refer to the person making the document as a "declarant." A declarant must be mentally competent at the time of signing a living will.
A person who signs a statement or declaration alleging that the information contained in the statement is true. Compare: affiant
a person who declares or makes a declaration or statement. · an alien who has formally declared his or her intention before a court of record to become a citizen of the U.S.