Whist variant (4)
I believe the answer is:
solo
'whist variant' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for solo that I've seen before include "Han - (Star Wars); fly unaccompanied" , "Unaccompanied, musically or on adventure" , "Card game; for one" , "By oneself" , "Lone" .)