Synonyms for Soften (same or very similar meaning)
WordNet sense 1 (give in, as to influence or pressure):
relent, yieldWordNet sense 2 (protect from impact):
buffer, cushionWordNet sense 3 (make less severe or harsh):
mince, moderate, moderateWordNet sense 4 (lessen in force or effect):
break, damp, dampen, weakenFrom the ODE community, based on WordNetadd/edit