Source : Webster's Revised Unabridged Dictionary (1913)

Twice \Twice\, adv. [OE. twies (where the s is the adverbial
   ending; see {-wards}), twie, AS. twiges, twiwa; akin to twi-
   (in comp.) two, G. zwie-, OHG. zwi-, Icel. tv[=i]-, L. bi-,
   Gr. ?, Skr. dvi-, and E. two. See {Two}.]
   1. Two times; once and again.

            He twice essayed to cast his son in gold. --Dryden.

   2. Doubly; in twofold quantity or degree; as, twice the sum;
      he is twice as fortunate as his neighbor.

   Note: Twice is used in the formation of compounds, mostly
         self-explaining; as, twice-horn, twice-conquered,
         twice-planted, twice-told, and the like.

Source : WordNet®

twice
     adv 1: two times; "I called her twice"
     2: to double the degree; "she was doubly rewarded"; "his eyes
        were double bright" [syn: {doubly}, {double}]