Come across excellent friend (7)
I believe the answer is:
comrade
'friend' is the definition.
(I know that comrade is a type of friend)
'come across excellent' is the wordplay.
'across' indicates putting letters inside.
'excellent' becomes 'rad' (slang term).
'come' going around 'rad' is 'COMRADE'.
(Other definitions for comrade that I've seen before include "Fellow-soldier" , "Companion" , "Ally" , "Fellow soldier" , "Fellow left-winger" .)