Endlessly criticise hot couple (6)
I believe the answer is:
attach
'couple' is the definition.
(I've seen this before)
'endlessly criticise hot' is the wordplay.
'endlessly' means to remove the last letter.
'criticise' becomes 'attack' (attacking is a kind of criticizing).
'hot' becomes 'h'.
'attack' with its final letter taken off is 'attac'.
'attac'+'h'='ATTACH'
(Other definitions for attach that I've seen before include "Append, join" , "Tie, bind to" , "Add on to, couple" , "Secure" , "Join or seize by law" .)