nearly vs nigh

nearly is not an adjective while nigh is an adjective.

Word	Noun	Adjective	Verb	Adverb
nearly	No	No	No	Yes
nigh	No	Yes	No	Yes

As adverbs, nearly and nigh are synonyms defined as:

nearly and nigh: (of actions or states) slightly short of or not quite accomplished; all but

Other synonyms of nearly include about, almost, most, near, virtually, well-nigh.

nearly (adjective)	nigh (adjective)
	not far distant in time or space or degree or circumstances
	being on the left side

nearly (adverb)	nigh (adverb)
(of actions or states) slightly short of or not quite accomplished; all but	near in time or place or relationship
in a close manner	(of actions or states) slightly short of or not quite accomplished; all but