second-best vs best

second-best is not a noun while best is a noun.

Word	Noun	Adjective	Verb	Adverb
second-best	No	Yes	No	Yes
best	Yes	Yes	Yes	Yes

second-best (noun)	best (noun)
	the supreme effort one can make
	the person who is most outstanding or excellent; someone who tops all others

second-best (adjective)	best (adjective)
next to the best	(superlative of `good') having the most positive qualities
	(comparative and superlative of `well') wiser or more advantageous and hence advisable

second-best (verb)	best (verb)
	get the better of

second-best (adverb)	best (adverb)
in second place	it would be sensible
	in a most excellent way or manner
	from a position of superiority or authority