Experts playing cards (4)
I believe the answer is:
aces
I believe this is a double definition.
'experts' is the first definition.
(ace is a kind of expert)
'playing cards' is the second definition.
(ace is a kind of playing card)
(Other definitions for aces that I've seen before include "Top (or bottom) cards" , "winning shots" , "Playing cards with single pips on their faces" , "Two will make deuce" , "Top cards or people" .)