1. To make hard or harder; to make firm or compact; to indurate; as, to harden clay or iron. 2. To accustom by labor or suffering to endure with constancy; to strengthen; to stiffen; to inure; also, to confirm in wickedness or shame; to make unimpressionable. "Harden not your heart." Ps. xcv. 8. I would harden myself in sorrow. Job ...