harden (
http://definr.com/harden)
v 1: become hard or harder; "The wax hardened" [ant:
soften]
2: make hard or harder; "The cold hardened the butter" [ant:
soften]
3: harden by reheating and cooling in oil; "temper steel" [syn:
temper]
4: make fit; "This trip will season even the hardiest
traveller" [syn:
season]
5: cause to accept or become hardened to; habituate; "He was
inured to the cold" [syn:
inure]