Couple I came upon heading west (4)
I believe the answer is:
item
'couple' is the definition.
(I've seen this before)
'i came upon heading west' is the wordplay.
'came' becomes 'met' (meeting is a kind of coming).
'upon' is a charade indicator (letters next to each other).
'heading west' is a reversal indicator.
'i' put after 'met' is 'meti'.
'meti' reversed gives 'ITEM'.
(Other definitions for item that I've seen before include "Boyfriend and girlfriend" , "Single unit" , "two with a link" , "Object in a list" , "Also no more" .)