Source : Webster's Revised Unabridged Dictionary (1913)

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.

   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.

   Syn: Deposition. See {Deposition}.

Source : WordNet®

affidavit
     n : written declaration made under oath; a written statement
         sworn to be true before someone legally authorized to
         administer an oath