WordNet (r) 3.0 (2006):

well-defined
    adj 1: having a clean and distinct outline as if precisely cut
           along the edges; "a finely chiseled nose"; "well-defined
           features" [syn: chiseled, well-defined]
    2: accurately stated or described; "a set of well-defined
       values" [syn: well-defined, clear] [ant: ill-defined,
       unclear]

Moby Thesaurus II by Grady Ward, 1.0:

46 Moby Thesaurus words for "well-defined":
   clean-cut, clear, clear as crystal, clear as day, clear-cut,
   coherent, connected, consistent, conspicuous, crisp, crystal-clear,
   crystalline, defined, definite, direct, distinct, evident,
   explicit, express, glaring, in focus, limpid, loud and clear,
   lucid, luminous, obvious, patent, pellucid, perspicuous, plain,
   prominent, pronounced, simple, staring, straightforward,
   translucent, transparent, transpicuous, unambiguous, unconfused,
   unequivocal, univocal, unmistakable, well-marked, well-pronounced,
   well-resolved