The Collaborative International Dictionary of English v.0.48:

Vagina \Va*gi"na\, n.; pl. Vaginae. [L. vagina a scabbard or
   sheath.]
   [1913 Webster]
   1. (Anat.)
      (a) A sheath; a theca; as, the vagina of the portal vein.
      (b) Specifically, the canal which leads from the uterus to
          the external orifice of the genital canal, or to the
          cloaca.
          [1913 Webster]

   2. (Zool.) The terminal part of the oviduct in insects and
      various other invertebrates. See Illust., of
      Spermatheca.
      [1913 Webster]

   3. (Bot.) The basal expansion of certain leaves, which
      inwraps the stem; a sheath.
      [1913 Webster]

   4. (Arch.) The shaft of a terminus, from which the bust or
      figure seems to issue or arise.
      [1913 Webster]

WordNet (r) 3.0 (2006):

vagina
    n 1: the lower part of the female reproductive tract; a moist
         canal in female mammals extending from the labia minora to
         the uterus; "the vagina receives the penis during coitus";
         "the vagina is elastic enough to allow the passage of a
         fetus"

Moby Thesaurus II by Grady Ward, 1.0:

62 Moby Thesaurus words for "vagina":
   Eustachian tube, Fallopian tube, bag, ballocks, balls, basket,
   beard, breasts, canal, cervix, clitoris, cod, cods, cullions, duct,
   emunctory, family jewels, female organs, fistula, genitalia,
   genitals, gonads, intestines, labia, labia majora, labia minora,
   lingam, lips, male organs, meat, meatus, nuts, nymphae, ostium,
   ovary, oviduct, penis, phallus, pore, private parts, privates,
   privy parts, pubic hair, pudenda, reproductive organs, rocks,
   salpinx, scrotum, secondary sex characteristic, sex organs,
   spermary, testes, testicles, thoracic duct, ureter, urethra,
   uterus, vas, vessel, vulva, womb, yoni