almost vs nigh

almost is not an adjective while nigh is an adjective.

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

As adverbs, almost and nigh are synonyms defined as:

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

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

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

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