Primo (4)
(Other definitions for aces that I've seen before include "Ones or elevens in cards" , "Case of top cards" , "Tennis serves the receiver can't reach" , "Two will make deuce" , "wartime pilots?" .)
'primo' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for grade a that I've seen before include "Top quality or classification" , "Top quality in alphabetic designation" , "Best quality" .)