The Collaborative International Dictionary of English v.0.48:

Vestal \Ves"tal\, a. [L. Vestalis belonging to Vesta, vestal.
   See Vesta.]
   Of or pertaining to Vesta, the virgin goddess of the hearth;
   hence, pure; chaste.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Vestal \Ves"tal\, n. [L. Vestalis (sc. virgo): cf. F. vestale.
   See Vestal, a.]
   1. (Rom. Antiq.) A virgin consecrated to Vesta, and to the
      service of watching the sacred fire, which was to be
      perpetually kept burning upon her altar.
      [1913 Webster]

   Note: The Vestals were originally four, but afterward six, in
         number. Their term of service lasted thirty years, the
         period of admission being from the sixth to the tenth
         year of the candidate's age.
         [1913 Webster]

   2. A virgin; a woman pure and chaste; also, a nun.
      [1913 Webster]

            How happy is the blameless vestal's lot! --Pope.
      [1913 Webster]

WordNet (r) 3.0 (2006):

vestal
    adj 1: of or relating to Vesta; "vestal virgin"
    2: in a state of sexual virginity; "pure and vestal modesty"; "a
       spinster or virgin lady"; "men have decreed that their women
       must be pure and virginal" [syn: pure, vestal, virgin,
       virginal, virtuous]
    n 1: a chaste woman

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "vestal":
   Platonic, abstinent, bachelor girl, celibate, continent, feme sole,
   intact, lone woman, maid, maiden, maiden lady, maidenly, old maid,
   single girl, spinster, spinstress, vestal virgin, virgin,
   virginal