trivial vs niggling

trivial and niggling both are adjectives.

Word	Noun	Adjective	Verb	Adverb
trivial	No	Yes	No	No
niggling	No	Yes	No	No

As adjectives, trivial and niggling are synonyms defined as:

Other synonyms of trivial include fiddling, footling, lilliputian, little, petty, picayune, piddling, piffling.

trivial (adjective)	niggling (adjective)
concerned with trivialities	(informal) small and of little importance
of little substance or significance
(informal) small and of little importance