High or low card (3)
I believe the answer is:
ace
'high or low card' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ace that I've seen before include "Hole in one; card" , "Tennis serve that the opponent can't reach" , "Player who excels" , "Winning serve; hole in one" , "Entertain" .)