Cold shoulder sent back before relations eat (4,2)
I believe the answer is:
tuck in
'eat' is the definition.
(I've seen this before)
'cold shoulder sent back before relations' is the wordplay.
'cold shoulder' becomes 'cut' ('cut' can be a synonym of 'cold shoulder').
'sent back' says the letters should be written backwards.
'before' means one lot of letters go next to another.
'relations' becomes 'kin' (I've seen this before).
'cut' written backwards gives 'tuc'.
'tuc'+'kin'='TUCK-IN'
(Other definitions for tuck in that I've seen before include "Arrange comfortable retirement" , "have hearty meal" , "Eat heartily" , "Go ahead and eat!" , "Substantial meal" .)