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1. Become hard or harder
   "The wax hardened";
   - indurate
    
2. Make hard or harder
   "The cold hardened the butter";
   - indurate
    
3. Harden by reheating and cooling in oil
   "harden steel";
   - temper
    
4. Make fit
   "This trip will harden even the hardiest traveller";
   - season
    
5. Cause to accept or become hardened to; habituate
   "He was hardened to the cold";
   - inure, indurate, enure

Derived forms: hardened, hardens, hardening

Type of: accustom, change, habituate, modify, toughen

Antonym: soften

Encyclopedia: Harden, Walsall