Source : Webster's Revised Unabridged Dictionary (1913)

Photo-epinasty \Pho`to-ep"i*nas`ty\, n. [See {Photo-}, and
   {Epinastic}.] (Bot.)
   A disproportionately rapid growth of the upper surface of
   dorsiventral organs, such as leaves, through the stimulus of
   exposure to light. --Encyc. Brit.