#1 harden v. [indurate] become hard or harder; "The wax hardened". wn
#2 harden v. [indurate] make hard or harder; "The cold hardened the butter". wn
#3 harden v. [temper] harden by reheating and cooling in oil; "temper steel". wn
#4 harden v. [season] make fit; "This trip will season even the hardiest traveller". wn
#5 harden v. [inure, indurate] cause to accept or become hardened to; habituate; "He was inured to the cold". wn
vizzz