best vs second-best

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

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

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

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

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

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