To make hard or more hard in substance or texture; make firm or compact; indurate: as, to harden steel, clay, or tallow; to harden the hands or muscles by toil.To dry (clothes) by airing.To make hard or harder in feeling; strengthen or confirm with respect to any element of character; inure; toughen; especially, to make indifferent, unfeeling, obstinate, wicked, etc.Synonyms To accustom, discipline, train, toughen, habituate, steel, brace, nerve.To become hard or more hard; acquire solidity or compactness: as, mortar hardens in drying.To become inured or toughened; especially, to become unfeeling.To rise in price; grow dear: as, the market hardens.Of hards or inferior flax.n. Hards or inferior flax.n. A cloth of coarse fiber and texture, made from hards.