Synonyms for Harden (same or very similar meaning)
WordNet sense 1 (make hard or harder):
indurateWordNet sense 2 (harden by reheating and cooling in oil):
temperWordNet sense 3 (make fit):
seasonWordNet sense 4 (cause to accept or become hardened to; habituate):
inureFrom the ODE community, based on WordNetadd/edit