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]

The Collaborative International Dictionary of English v.0.48:

Niggle \Nig"gle\, v. i.
   1. To trifle or play.
      [1913 Webster]

            Take heed, daughter,
            You niggle not with your conscience and religion.
                                                  --Massinger.
      [1913 Webster]

   2. To act or walk mincingly. [Prov. Eng.]
      [1913 Webster]

   3. To fret and snarl about trifles. [Prov. Eng.]
      [1913 Webster]

   4. (Chiefly Eng.)

   1. To move about restlessly or without result; to fidget.
      [Webster 1913 Suppl.]

   5. To be finicky or excessively critical; to potter; esp., to
      work with excessive care for trifling details, as in
      painting.
      [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Niggle \Nig"gle\, v. t.
   1. To use, spend, or do in a petty or trifling manner.
      [Webster 1913 Suppl.]

   2. To elaborate excessively, as in art.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

niggle
    v 1: worry unnecessarily or excessively; "don't fuss too much
         over the grandchildren--they are quite big now" [syn:
         fuss, niggle, fret]
    2: argue over petty things; "Let's not quibble over pennies"
       [syn: quibble, niggle, pettifog, bicker, squabble,
       brabble]

Moby Thesaurus II by Grady Ward, 1.0:

62 Moby Thesaurus words for "niggle":
   adverse criticism, animadversion, aspersion, bad notices,
   bad press, bitch, bug, captiousness, carp, carp at, carping, cavil,
   caviling, censoriousness, complain, criticism, criticize,
   exception, faultfinding, find fault, flak, fret at, fuss, fuss at,
   grouse, hairsplitting, hassle, henpeck, hit, home thrust,
   hostile criticism, hypercriticalness, hypercriticism, imputation,
   knock, kvetch, nag, nagging, nibble at, niggling, nit, nit-picking,
   obloquy, overcriticalness, peck at, pester, pestering,
   pettifogging, pick at, pick on, priggishness, quibble, quibbling,
   rap, reflection, reproachfulness, slam, stricture, swipe,
   taking exception, trichoschistism, yap at