contend vs niggle

contend and niggle both are verbs.

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

As verbs, niggle is a hyponym of contend; that is, niggle is a word with a more specific, narrower meaning than contend:

contend (verb)	niggle (verb)
to make the subject of dispute, contention, or litigation	argue over petty things
have an argument about something	worry unnecessarily or excessively
maintain or assert
compete for something; engage in a contest; measure oneself against others
be engaged in a fight; carry on a fight
succeed in doing, achieving, or producing (something) with the limited or inadequate means available