The Collaborative International Dictionary of English v.0.48:

Niggling \Nig"gling\, a.
   1. petty, trivial, or inconsequential.
      [PJC]

   2. Excessively demanding of time or attention; as, niggling
      little details.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

niggling \nig"gling\, n.
   Finicky or pottering work; specif. (Fine Arts), Minute and
   very careful workmanship in drawing, painting, or the like,
   esp. when bestowed on unimportant detail.
   [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Niggle \Nig"gle\, v. t. [imp. & p. p. Niggled; p. pr. & vb. n.
   Niggling.] [Dim. of Prov. E. nig to clip money; cf. also
   Prov. E. nig a small piece.]
   To trifle with; to deceive; to mock. [Obs.] --Beau. & Fl.
   [1913 Webster]

WordNet (r) 3.0 (2006):

niggling
    adj 1: (informal) small and of little importance; "a fiddling
           sum of money"; "a footling gesture"; "our worries are
           lilliputian compared with those of countries that are at
           war"; "a little (or small) matter"; "a dispute over
           niggling details"; "limited to petty enterprises";
           "piffling efforts"; "giving a police officer a free meal
           may be against the law, but it seems to be a picayune
           infraction" [syn: fiddling, footling, lilliputian,
           little, niggling, piddling, piffling, petty,
           picayune, trivial]

Moby Thesaurus II by Grady Ward, 1.0:

115 Moby Thesaurus words for "niggling":
   Mickey Mouse, adverse criticism, advertent, agog, alert, all ears,
   all eyes, animadversion, annoying, aspersion, assiduous, attentive,
   aware, bad notices, bad press, captious, captiousness, careful,
   carping, cavil, caviling, censoriousness, concentrated, conscious,
   critical, criticism, cynical, diligent, earnest, exception,
   faultfinding, finical, finicking, finicky, flak, frivolous, fussy,
   hairsplitting, heedful, hit, home thrust, hostile criticism,
   hypercritical, hypercriticalness, hypercriticism, imputation,
   inconsequential, insignificant, intense, intent, intentive,
   irksome, irritating, jerkwater, knock, measly, meticulous, mindful,
   nagging, nice, niggle, nit, nit-picking, nugatory, obloquy,
   observant, observing, on the ball, on the job, one-horse,
   open-eared, open-eyed, openmouthed, overcritical, overcriticalness,
   paltry, peanut, pestering, pettifogging, petty, picayune,
   picayunish, piddling, piffling, poky, priggishness, punk, puny,
   quibble, quibbling, rap, reflection, regardful, reproachfulness,
   slam, small-beer, small-time, stricture, swipe, taking exception,
   tinhorn, trichoschistic, trichoschistism, trifling, trivial,
   troublesome, two-bit, two-by-four, ultracritical, unimportant,
   vexatious, vexing, watchful, worrisome, worrying