second best vs competition

second best and competition both are nouns.

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

As nouns, competition is a hypernym of second best; that is, competition is a word with a broader meaning than second best:

Other hypernyms of second best include challenger, competitor, contender, rival.

second best (noun)	competition (noun)
the competitor who finishes second	the act of competing as for profit or a prize
	an occasion on which a winner is selected from among two or more contestants
	the contestant you hope to defeat
	a business relation in which two parties compete to gain customers