well-nigh vs nearly

well-nigh and nearly both are adverbs.

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

As adverbs, well-nigh and nearly are synonyms defined as:

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

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

well-nigh (adverb)	nearly (adverb)
(of actions or states) slightly short of or not quite accomplished; all but	(of actions or states) slightly short of or not quite accomplished; all but
	in a close manner