The Collaborative International Dictionary of English v.0.48:

Harden \Hard"en\, v. i.
   1. To become hard or harder; to acquire solidity, or more
      compactness; as, mortar hardens by drying.
      [1913 Webster]

            The deliberate judgment of those who knew him [A.
            Lincoln] has hardened into tradition. --The Century.
      [1913 Webster]

   2. To become confirmed or strengthened, in either a good or a
      bad sense.
      [1913 Webster]

            They, hardened more by what might most reclaim.
                                                  --Milton.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Harden \Hard"en\ (h[aum]rd"'n), v. t. [imp. & p. p. Hardened
   (-'nd); p. pr. & vb. n. Hardening (-'n*[i^]ng).] [OE.
   hardnen, hardenen.]
   1. To make hard or harder; to make firm or compact; to
      indurate; as, to harden clay or iron.
      [1913 Webster]

   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.
      [1913 Webster]

            I would harden myself in sorrow.      --Job vi. 10.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Hurden \Hur"den\, n. [From Hurds.]
   A coarse kind of linen; -- called also harden. [Prov. Eng.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

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

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "harden":
   acclimate, acclimatize, accommodate, accustom, adapt, adjust,
   anneal, be tough, beef up, brace, brace up, break, break in,
   brutalize, buttress, cake, calcify, callous, case harden,
   caseharden, compact, concrete, condition, confirm, conform,
   congeal, consolidate, cornify, crystallize, densify, domesticate,
   domesticize, dry, endure, establish, familiarize, firm, fix,
   fortify, fossilize, freeze, gentle, gird, habituate, hang tough,
   housebreak, indurate, intensify, inure, invigorate, lapidify,
   lithify, naturalize, nerve, orient, orientate, ossify, petrify,
   prop, refresh, reinforce, reinvigorate, restrengthen, season, set,
   shore up, solidify, steel, stiffen, strengthen, support, sustain,
   tame, temper, toughen, train, turn to stone, undergird, vitrify,
   wont