[syn: tempered, treated, hardened, toughened]
The Collaborative International Dictionary of English v.0.48:
Toughen \Tough"en\, v. i. & t. [imp. & p. p. Toughened; p. pr.
   & vb. n. Toughening.]
   To grow or make tough, or tougher.
   [1913 Webster]
WordNet (r) 3.0 (2006):
toughened
    adj 1: physically toughened; "the tough bottoms of his feet"
           [syn: tough, toughened] [ant: tender,
           untoughened]
    2: made hard or flexible or resilient especially by heat
       treatment; "a sword of tempered steel"; "tempered glass"
       [syn: tempered, treated, hardened, toughened] [ant:
       unhardened, untempered]
Moby Thesaurus II by Grady Ward, 1.0:
29 Moby Thesaurus words for "toughened":
   annealed, backed, calcified, callous, calloused, case-hardened,
   crusted, crusty, crystallized, fossilized, granulated, hardened,
   hornified, incrusted, indurate, indurated, lapidified, ossified,
   petrified, reinforced, rigidified, sclerotic, set, solidified,
   steeled, stiffened, strengthened, tempered, vitrified