Toughen

Verb

 * 1)  To make tough.
 * 2)  To become tough.

Thesaurus
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