The Collaborative International Dictionary of English v.0.48:

Define \De*fine"\, v. t. [imp. & p. p. Defined; p. pr. & vb.
   n. Defining.] [OE. definer, usually, to end, to finish, F.
   d['e]finir to define, L. definire to limit, define; de- +
   finire to limit, end, finis boundary, limit, end. See
   Final, Finish.]
   1. To fix the bounds of; to bring to a termination; to end.
      "To define controversies." --Barrow.
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   2. To determine or clearly exhibit the boundaries of; to mark
      the limits of; as, to define the extent of a kingdom or
      country.
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   3. To determine with precision; to mark out with
      distinctness; to ascertain or exhibit clearly; as, the
      defining power of an optical instrument.
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            Rings . . . very distinct and well defined. --Sir I.
                                                  Newton.
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   4. To determine the precise signification of; to fix the
      meaning of; to describe accurately; to explain; to expound
      or interpret; as, to define a word, a phrase, or a
      scientific term.
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            They define virtue to be life ordered according to
            nature.                               --Robynson
                                                  (More's
                                                  Utopia).
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WordNet (r) 3.0 (2006):

defined
    adj 1: clearly characterized or delimited; "lost in a maze of
           words both defined and undefined"; "each child has
           clearly defined duties" [ant: undefined, vague]
    2: showing clearly the outline or profile or boundary; "hills
       defined against the evening sky"; "the setting sun showed the
       outlined figure of a man standing on the hill" [syn:
       defined, outlined]

Moby Thesaurus II by Grady Ward, 1.0:

83 Moby Thesaurus words for "defined":
   absolute, certain, circumscribed, circumscript, clean-cut, clear,
   clear as crystal, clear as day, clear-cut, coherent, concrete,
   connected, consistent, conspicuous, crisp, crystal-clear,
   crystalline, definite, delimited, demarcated, detailed,
   determinate, determined, different, direct, distinct,
   distinguished, encircled, esoteric, especial, evident, exceptional,
   explicit, express, extraordinary, fixed, glaring, hedged about,
   in focus, individual, inner, intimate, limpid, loud and clear,
   lucid, luminous, minute, noteworthy, obvious, particular, patent,
   pellucid, personal, perspicuous, plain, precise, private,
   prominent, pronounced, respective, set, several, simple, singular,
   solipsistic, special, specific, staring, stated, straightforward,
   surrounded, translucent, transparent, transpicuous, unambiguous,
   unconfused, unequivocal, univocal, unmistakable, well-defined,
   well-marked, well-pronounced, well-resolved