verb
1.
to make or become physically hard or solid
this substance hardens immediately on exposure to air
Synonyms: cake, concrete, congeal, dry, indurate, set, solidify
Related Word: compact, consolidate, densify, firm, stiffen; anneal, caseharden, temper; calcify, fossilize, lithify, ossify, petrify
Contrasted words: deliquesce, dissolve, fuse, liquefy, melt
Antonyms: soften
2.
to make proof against hardship, strain, or exposure
frontier life hardened most men quickly to rough conditions
Synonyms: acclimate, acclimatize, climatize, season, toughen
Related Word: accustom, habituate, indurate, inure; accommodate, adapt, adjust, conform
Contrasted words: emasculate, enervate; debilitate, devitalize, enfeeble, sap, undermine, weaken
Antonyms: soften