Source : Webster's Revised Unabridged Dictionary (1913)

Bigamy \Big"a*my\, n. [OE. bigamie, fr. L. bigamus twice
   married; bis twice + Gr. ? marriage; prob. akin to Skt.
   j[=a]mis related, and L. gemini twins, the root meaning to
   bind, join: cf. F. bigamie. Cf. {Digamy}.] (Law)
   The offense of marrying one person when already legally
   married to another. --Wharton.

   Note: It is not strictly correct to call this offense bigamy:
         it more properly denominated polygamy, i. e., having a
         plurality of wives or husbands at once, and in several
         statutes in the United States the offense is classed
         under the head of polygamy. In the canon law bigamy was
         the marrying of two virgins successively, or one after
         the death of the other, or once marrying a widow. This
         disqualified a man for orders, and for holding
         ecclesiastical offices. Shakespeare uses the word in
         the latter sense. --Blackstone. --Bouvier.

               Base declension and loathed bigamy. --Shak.

Source : WordNet®

bigamy
     n 1: having two spouses at the same time
     2: the offense of marrying someone while you have a living
        spouse from whom no valid divorce has occurred