NOUN (1)

1. written declaration made under oath; a written statement sworn to be true before someone legally authorized to administer an oath;

The Collaborative International Dictionary of English v.0.48:

Affidavit \Af`fi*da"vit\, n. [LL. affidavit he has made oath,
   perfect tense of affidare. See Affiance, Affy.] (Law)
   A sworn statement in writing; a declaration in writing,
   signed and made upon oath before an authorized magistrate.
   --Bouvier. --Burrill.
   [1913 Webster]

   Note: It is always made ex parte, and without
         cross-examination, and in this differs from a
         deposition. It is also applied to written statements
         made on affirmation.
         [1913 Webster]

   Syn: Deposition. See Deposition.
        [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "affidavit":
   admission, affirmation, allegation, assertion, asseveration,
   attest, attestation, authority, authorization, averment,
   avouchment, avowal, bill, bill of complaint, bill of health,
   certificate, certificate of proficiency, certification, claim,
   complaint, compurgation, credential, declaration, deposition,
   diploma, disclosure, instrument in proof, legal evidence, libel,
   manifesto, narratio, navicert, nolle prosequi, nonsuit,
   notarized statement, note, position paper, profession, sheepskin,
   solemn declaration, statement, statement of belief,
   statement of facts, statement under oath, swearing, sworn evidence,
   sworn statement, sworn testimony, testamur, testimonial,
   testimonium, testimony, ticket, visa, vise, voucher, vouching,
   warrant, warranty, witness, word