The Collaborative International Dictionary of English v.0.48:

Aunt \Aunt\, n. [OF. ante, F. tante, L. amita father's sister.
   Cf. Amma.]
   1. The sister of one's father or mother; -- correlative to
      nephew or niece. Also applied to an uncle's wife.
      [1913 Webster]

   Note: Aunt is sometimes applied as a title or term of
         endearment to a kind elderly woman not thus related.
         [1913 Webster]

   2. An old woman; and old gossip. [Obs.] --Shak.
      [1913 Webster]

   3. A bawd, or a prostitute. [Obs.] --Shak.
      [1913 Webster]

   Aunt Sally, a puppet head placed on a pole and having a
      pipe in its mouth; also a game, which consists in trying
      to hit the pipe by throwing short bludgeons at it.
      [1913 Webster]

WordNet (r) 3.0 (2006):

aunt
    n 1: the sister of your father or mother; the wife of your uncle
         [syn: aunt, auntie, aunty] [ant: uncle]

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "aunt":
   auntie, blood brother, brethren, brother, bub, bubba, bud, buddy,
   country cousin, cousin, cousin once removed, cousin twice removed,
   daughter, father, first cousin, foster brother, frater,
   grandnephew, grandniece, granduncle, great-aunt, great-uncle,
   half brother, kid brother, mother, nephew, niece, nuncle, nunks,
   nunky, second cousin, sis, sissy, sister, sister-german, sistern,
   son, stepbrother, stepsister, unc, uncle, uncs, uterine brother



Bouvier's Law Dictionary, Revised 6th Ed (1856):

AUNT, domestic relations. The sister of one's father or mother; she is a
relation in the third degree. Vide 2 Com. Dig. 474 Dane's Ab. c. 126, a. 3.
Sec. 4.