Separate unit for couple linked (4)
I believe the answer is:
item
This clue is a double definition.
'separate unit' is the first definition.
(I've seen this before)
'couple linked' is the second definition.
(I've seen this before)
'for' acts as a link.
(Other definitions for item that I've seen before include "Bit of information" , "One article" , "Piece in paper" , "Romantic couple" , "Component" .)