say it: HAHR-duhn
harden is a verb meaning "become hard or harder". It carries 5 recorded senses.
cause to accept or become hardened to; habituate
“He was inured to the cold”
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for harden come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.