Source : Webster's Revised Unabridged Dictionary (1913)

Anthesis \An*the"sis\, n. [Gr. ? bloom, fr. 'anqei^n to bloom,
   'a`nqos flower.] (Bot.)
   The period or state of full expansion in a flower. --Gray.

Source : WordNet®

anthesis
     n : the time and process of budding and unfolding of blossoms
         [syn: {blossoming}, {flowering}, {florescence}, {inflorescence},
          {efflorescence}]