One first-class (3)
I believe the answer is:
ace
I believe this clue is a double definition.
'one' is the first definition.
(ace has a value of one in some card games)
'first-class' is the second definition.
(synonyms)
(Other definitions for ace that I've seen before include "Unreturnable serve" , "Adept" , "Playing card with single spot" , "even higher than the king" , "Crack" .)