The Collaborative International Dictionary of English v.0.48:

Fastidious \Fas*tid"i*ous\, a. [L. fastidiosus disdainful, fr.
   fastidium loathing, aversion, perh. fr. fastus arrogance (of
   uncertain origin) + taedium loathing. Cf. Tedious, Fash.]
   Difficult to please; delicate to a fault; suited with
   difficulty; squeamish; as, a fastidious mind or ear; a
   fastidious appetite.
   [1913 Webster]

         Proud youth ! fastidious of the lower world. --Young.

   Syn: Squeamish; critical; overnice; difficult; punctilious.


   Usage: Fastidious, Squeamish. We call a person fastidious
          when his taste or feelings are offended by trifling
          defects or errors; we call him squeamish when he is
          excessively nice or critical on minor points, and also
          when he is overscrupulous as to questions of duty.
          "Whoever examines his own imperfections will cease to
          be fastidious; whoever restrains his caprice and
          scrupulosity will cease to be squeamish." --Crabb. --
          Fas*tid"i*ous*ly, adv. -- Fas*tid"i*ous*ness, n.
          Fastigiate

WordNet (r) 3.0 (2006):

fastidious
    adj 1: giving careful attention to detail; hard to please;
           excessively concerned with cleanliness; "a fastidious and
           incisive intellect"; "fastidious about personal
           cleanliness" [ant: unfastidious]
    2: having complicated nutritional requirements; especially
       growing only in special artificial cultures; "fastidious
       microorganisms"; "certain highly specialized xerophytes are
       extremely exacting in their requirements" [syn: fastidious,
       exacting] [ant: unfastidious]

Moby Thesaurus II by Grady Ward, 1.0:

99 Moby Thesaurus words for "fastidious":
   accurate, appreciative, bleached, bright, careful, censorious,
   choicy, choosy, civilized, clean, cleanly, conscientious, critical,
   cultivated, cultured, dainty, delicate, differential, difficult,
   dirt-free, discriminate, discriminating, discriminative,
   distinctive, distinguishing, elegant, exact, exacting, fair, fine,
   finical, finicky, fresh, fussy, graceful, gracile, gracious,
   hypercritical, immaculate, kosher, meticulous, nice, nit-picking,
   nonpolluted, of cleanly habits, overconscientious, overscrupulous,
   particular, perfectionistic, picky, polished, precise,
   precisianistic, priggish, prudish, punctilious, punctual, pure,
   puristic, puritanic, refined, religious, ritually pure, scrupulous,
   selective, sensitive, shiny, smut-free, smutless, sophisticated,
   spotless, squeamish, stainless, strict, subtle, sweet, tactful,
   tahar, tender-conscienced, tubbed, unadulterated, unbesmirched,
   unblemished, unblotted, undefiled, unmuddied, unpolluted,
   unsmirched, unsmudged, unsoiled, unspotted, unstained, unsullied,
   untainted, untarnished, well-scrubbed, well-washed, white,
   whitened