acclimate, acclimatize, anneal, be tough, beef up, brace, brace up, buttress, calcify, callous, case harden, confirm, cornify, develop, endure, firm, fortify, fossilize, gird, hang tough, harden, indurate, invigorate, lapidify, lithify, nerve, ossify, petrify, prop, refresh, reinforce, reinvigorate, restrengthen, season, shore up, steel, stiffen, strengthen, support, sustain, temper, undergird, vitrify