Everybody has yen for a friend (4)
I believe the answer is:
ally
'a friend' is the definition.
('ally' can be a synonym of 'friend')
'everybody has yen' is the wordplay.
'everybody' becomes 'all' (I've seen this before).
'has' says to put letters next to each other.
'yen' becomes 'y'.
'all'+'y'='ALLY'
'for' acts as a link.
(Other definitions for ally that I've seen before include "One co-operating with another" , "support" , "A friendly and reliable country" , "Join - friend" , "Cooperating country" .)