Add friend, absolutely (7)
I believe the answer is:
totally
'absolutely' is the definition.
(synonyms)
'add friend' is the wordplay.
'add' becomes 'tot' (synonyms).
'friend' becomes 'ally' (an ally is a friend or supporter).
'tot'+'ally'='TOTALLY'
(Other definitions for totally that I've seen before include "Utterly" , "Quite" , "without reservation" , "Absolutely" , "without reserve" .)