The Collaborative International Dictionary of English v.0.48:

Potentiate \Po*ten"ti*ate\, v. t. [imp. & p. p. Potentiated;
   p. pr. & vb. n. Potentiating.]
   To render active or potent. --Coleridge.
   [1913 Webster]

WordNet (r) 3.0 (2006):

potentiate
    v 1: increase the effect of or act synergistically with (a drug
         or a physiological or biochemical phenomenon); "potentiate
         the drug"