Cardinal participating in square dancing? (3)
I believe the answer is:
red
'cardinal' is the definition.
(I've seen this in other clues)
'participating in square dancing?' is the wordplay.
'participating in' indicates the answer is hidden within the clue.
'RED' is hidden within 'square dancing'.
(Other definitions for red that I've seen before include "Stop light" , "Colour for a blusher" , "lefty" , "Colour of a cardinal's hat" , "Glowing" .)