WordNet (r) 3.0 (2006):

tenderize
    v 1: make tender or more tender as by marinating, pounding, or
         applying a tenderizer; "tenderize meat" [syn: tender,
         tenderize, tenderise]

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "tenderize":
   cushion, ease, fluff, gentle, knead, laxate, limber, limber up,
   loosen, mash, massage, mellow, milden, mollify, plump, pulp, relax,
   shake up, smash, soften, soften up, squash, subdue, supple,
   tone down, tune down