Cups king and queen trade (6)
I believe the answer is:
barter
'trade' is the definition.
(I know that trade can be written as barter)
'cups king and queen' is the wordplay.
I cannot really see how this works, but
'king' could be 'er' (abbreviation for Edward Rex, various English kings) and 'er' is present in the answer.
'queen' could be 'r' (abbreviation for regina, e.g. in ER ) and 'r' is found within the answer.
The remaining letters 'bat' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for barter that I've seen before include "Trade by direct exchange of goods" , "Trade without using money" , "Trade not involving money" , "Exchange goods without using money" , "Trade, haggle" .)