Only one club in a suit! (6)
I believe the answer is:
hearts
This might be a double definition.
'only one club' is the first definition.
'hearts' can be an answer for 'club' (I've seen this before). I am unsure of the 'only one' bit.
'a suit' is the second definition.
(I've seen this before)
'in' is the link.
Can you help me to learn more?
(Other definitions for hearts that I've seen before include "Scottish team" , "Card suits in bodies" , "Suit for vital organs" , "Cores" , "Major suit at cards" .)