Flexible blackjack card (3)
I believe the answer is:
ace
'flexible blackjack card' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ace that I've seen before include "One-spotted card" , "reason for point of no return" , "Top playing card" , "Great" , "Tennis serve that the opponent can't reach" .)