piddling vs niggling

piddling and niggling both are adjectives.

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

As adjectives, piddling and niggling are synonyms defined as:

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

piddling (adjective)	niggling (adjective)
(informal) small and of little importance	(informal) small and of little importance