1. To make hard or harder; to make firm or compact; to indurate; as, to harden clay or iron. 2. To accustom by labour 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. I would harden myself in sorrow. (job vi. 10) Origin: oe. Hardnen, hardenen.