The Collaborative International Dictionary of English v.0.48:

Maidenhead \Maid"en*head\, n. [See Maidenhood.]
   1. The state of being a maiden; maidenhood; virginity.
      --Shak.
      [1913 Webster]

   2. The state of being unused or uncontaminated; freshness;
      purity. [Obs.]
      [1913 Webster]

            The maidenhead of their credit.       --Sir H.
                                                  Wotton.
      [1913 Webster]

   3. The hymen, or virginal membrane.
      [1913 Webster]

WordNet (r) 3.0 (2006):

maidenhead
    n 1: a fold of tissue that partly covers the entrance to the
         vagina of a virgin [syn: hymen, maidenhead, virginal
         membrane]

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "maidenhead":
   Platonic love, abstinence, allantoic membrane, amnion,
   amniotic sac, arachnoid membrane, bachelordom, bachelorhood,
   bachelorism, bachelorship, basement membrane, boyhood, celibacy,
   cherry, childhood, conjuctiva, continence, continency, eardrum,
   girlhood, hymen, intactness, maidenhood, membrana serosa,
   membrana tympana, membrane, meninges, meninx, misogamy, misogyny,
   monachism, monasticism, neurilemma, pellicle, pericardium,
   perineurium, pleura, pre-teens, serosa, single blessedness,
   single state, singleness, spinsterhood, subteens,
   tympanic membrane, tympanum, unwed state, velum, virgin state,
   virginity