Join for the whole year (4)
I believe the answer is:
ally
'join' is the definition.
(I've seen this before)
'the whole year' is the wordplay.
'the whole' becomes 'all' (I've seen this before).
'year' becomes 'y'.
'all'+'y'='ALLY'
'for' is the link.
(Other definitions for ally that I've seen before include "couple?" , "Supporter in a conflict" , "often helpful when cluing adverbs" , "support" , "State formally cooperating with another" .)