Read the dictionary definition of harden. All definitions for this word.
1. cause to accept or become hardened to; habituate
1. He was inured to the cold
2. make fit
1. This trip will season even the hardiest traveller
3. harden by reheating and cooling in oil
1. temper steel
4. become hard or harder
1. The wax hardened
5. make hard or harder
1. The cold hardened the butter