niggle vs worry

niggle is not a noun while worry is a noun.

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

As verbs, worry is a hypernym of niggle; that is, worry is a word with a broader meaning than niggle:

niggle (noun)	worry (noun)
	something or someone that causes anxiety; a source of unhappiness
	a strong feeling of anxiety

niggle (verb)	worry (verb)
argue over petty things	lacerate by biting
worry unnecessarily or excessively	touch or rub constantly
	be worried, concerned, anxious, troubled, or uneasy
	disturb the peace of mind of; afflict with mental agitation or distress
	be concerned with
	be on the mind of