bicker vs niggle

bicker is a noun but niggle is not a noun.

Word	Noun	Adjective	Verb	Adverb
bicker	Yes	No	Yes	No
niggle	No	No	Yes	No

As verbs, bicker and niggle are synonyms defined as:

Other synonyms of bicker include brabble, pettifog, quibble, squabble.

bicker (noun)	niggle (noun)
a quarrel about petty points

bicker (verb)	niggle (verb)
argue over petty things	argue over petty things
	worry unnecessarily or excessively