niggle (v.)

1590s (implied in niggling), "work in a finicky, fussy way; trifle, be employed in petty carping," a word of uncertain origin; possibly from a Scandinavian source (compare Norwegian dialectal nigla "be busy with trifles"), perhaps related to source of niggard. Related: Niggled; niggling; niggler.

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Definitions of niggle from WordNet

niggle (v.)
worry unnecessarily or excessively;
Synonyms: fuss / fret
niggle (v.)
argue over petty things;
Synonyms: quibble / pettifog / bicker / squabble / brabble
From wordnet.princeton.edu