harden

(verb) become hard or harder. Synonyms: indurate. Example: "The wax hardened."

(verb) make hard or harder. Synonyms: indurate. Example: "The cold hardened the butter."

(verb) harden by reheating and cooling in oil. Synonyms: temper. Example: "Temper steel."

(verb) make fit. Synonyms: season. Example: "This trip will season even the hardiest traveller."

(verb) cause to accept or become hardened to; habituate. Synonyms: inure, indurate. Example: "He was inured to the cold."