hardening
     n 1: abnormal hardening or thickening of tissue
     2: the process of becoming hard or solid by cooling or drying
        or crystallization; "the hardening of concrete"; "he
        tested the set of the glue" [syn: {solidifying}, {solidification},
         {set}, {curing}]
     3: the act of making something harder (firmer or tighter or
        more compact)
Source: WordNet® 2.0