Playing cards (4)
I believe the answer is:
aces
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">playing cards</span>' is the definition.<br/ ><span class="explanation-format__explanation">(ace is a kind of playing card)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for aces that I've seen before include "Top cards or people" , "Tennis serves the receiver can't reach" , "Winning serves" , "never come back" , "that are non-returnable" .)