The Collaborative International Dictionary of English v.0.48:

Hairsplitting \Hair"split`ting\ (-t[i^]ng), a.
   Making excessively fine or trivial distinctions in reasoning;
   overly subtle. -- n. The act or practice of making trivial
   distinctions.
   [1913 Webster]

         The ancient hairsplitting technicalities of special
         pleading.                                --Charles
                                                  Sumner.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hairsplitting
    adj 1: developed in excessively fine detail; "finespun
           distinctions" [syn: finespun, hairsplitting]
    n 1: making too fine distinctions of little importance; "they
         didn't take his hairsplitting seriously" [syn:
         hairsplitting, word-splitting]

Moby Thesaurus II by Grady Ward, 1.0:

119 Moby Thesaurus words for "hairsplitting":
   adverse criticism, animadversion, aspersion, bad notices,
   bad press, bickering, boggling, captious, captiousness, carping,
   cavil, caviling, censoriousness, chicane, chicanery, choplogic,
   contradistinction, critical, criticism, cynical, delicate,
   demarcation, differentiation, distinction, distinctiveness,
   distinguishment, division, dodging, equivocation, equivocatory,
   evasion, evasive, exception, faultfinding, fencing, finespun, flak,
   hairline, hedging, hit, home thrust, hostile criticism,
   hypercritical, hypercriticalness, hypercriticism, hypersensitive,
   hypersensitivity, imputation, knock, logic-chopping,
   microscopic distinction, morbid sensibility, morbidly sensitive,
   nagging, nice, nice distinction, niggle, niggling, nit,
   nit-picking, nuance, obloquy, overconscientious,
   overconscientiousness, overcritical, overcriticalness,
   overfastidious, overfastidiousness, overmeticulous,
   overmeticulousness, overnice, overniceness, overnicety,
   overparticular, overparticularity, overprecise, overrefined,
   overrefinement, overscrupulous, overscrupulousness, oversensitive,
   oversensitivity, oversqueamish, oversqueamishness, paltering,
   parrying, pestering, pettifoggery, pettifogging, petty, picayune,
   prevarication, priggishness, pussyfooting, quibble, quibbling, rap,
   refined, reflection, reproachfulness, segregation, separation,
   shade of difference, shifting, shuffling, sidestepping, slam,
   stricture, subterfuge, subtle, subtle distinction, swipe,
   taking exception, tergiversation, trichoschistic, trichoschistism,
   trifling, trivial, ultracritical