To the Yankee, everybody's a friend (4)
I believe the answer is:
ally
'a friend' is the definition.
(an ally is a friend or supporter)
'to the yankee everybody's' is the wordplay.
I cannot really understand how this works, but
'yankee' could be 'y' (phonetic alphabet: alpha, bravo, charlie etc.) and 'y' is located in the answer.
'everybody' could be 'all' (all people) and 'all' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for ally that I've seen before include "One co-operating with another" , "Associate that provides assistance" , "often helpful when cluing adverbs" , "couple?" , "Friend, partner" .)