Synonyms for harden Found 4 synonyms across 4 meanings for “harden”. become hard or harder (verb) indurate harden by reheating and cooling in oil (verb) temper make fit (verb) season cause to accept or become hardened to (verb) inure Explore Related Words Rhymes with hardenSynonyms for indurateSynonyms for temperSynonyms for seasonSynonyms for inure Synonym Finder | Rhyme Finder | Poetry Editor