Couple heads into the evening mist (4)
I believe the answer is:
item
'couple' is the definition.
(I've seen this before)
'heads into the evening mist' is the wordplay.
'heads' suggests taking the first letters.
The first letters of 'into the evening mist' is 'ITEM'.
(Other definitions for item that I've seen before include "point" , "Romantic couple" , "Separate article" , "Individual thing" , "One article" .)