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"