Source : Webster's Revised Unabridged Dictionary (1913)

Harden \Hard"en\, v. i.
   1. To become hard or harder; to acquire solidity, or more
      compactness; as, mortar hardens by drying.

            The deliberate judgment of those who knew him [A.
            Lincoln] has hardened into tradition. --The Century.

   2. To become confirmed or strengthened, in either a good or a
      bad sense.

            They, hardened more by what might most reclaim.
                                                  --Milton.

Harden \Hard"en\, v. t. [imp. & p. p. {Hardened}; p. pr. & vb.
   n. {Hardening}.] [OE. hardnen, hardenen.]
   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 vi. 10.

Source : WordNet®

harden
     v 1: become hard or harder; "The wax hardened" [syn: {indurate}]
          [ant: {soften}]
     2: make hard or harder; "The cold hardened the butter" [syn: {indurate}]
        [ant: {soften}]
     3: harden by reheating and cooling in oil; "temper steel" [syn:
         {temper}]
     4: make fit; "This trip will season even the hardiest
        traveller" [syn: {season}]
     5: cause to accept or become hardened to; habituate; "He was
        inured to the cold" [syn: {inure}, {indurate}]