I. ˌsecond ˈbest¹ noun [uncountable]
something that you have to accept which is not perfect or not the best:
I’m not going to settle for second best.

[TahlilGaran] Dictionary of Contemporary English ▲

II. ˌsecond ˈbest² adjective [only before noun], adverb
not quite as good as the best one:
Allie was the second best shooter on the rifle team.
come off second best (=lose a game or competition, or not be as successful as someone else)

[TahlilGaran] Dictionary of Contemporary English ▲

second best
something that is not as good as the thing that you really want.
I know exactly what sort of apartment I'm looking for and I'm not going to settle for second best.

[TahlilGaran] English Idioms Dictionary ▲

second best
adv. Second; in second place.
The team came off second best in the game.

[TahlilGaran] English Idioms Dictionary ▲

second best
adj. Next to best; second in rank.
Mary wore her second-best dress.
Bob was the second-best player on the team.
"I am the second-best student in this school because I was second best in the Milwaukee competition."

[TahlilGaran] English Idioms Dictionary ▲