Friend coming back with excellent computer (6)
I believe the answer is:
laptop
'computer' is the definition.
(laptop is a part of computer)
'friend coming back with excellent' is the wordplay.
'friend' becomes 'pal' (pal can mean a friend).
'coming back' is a reversal indicator.
'with' says to put letters next to each other.
'excellent' becomes 'top' (top can mean the best).
'pal' back-to-front is 'lap'.
'lap'+'top'='LAPTOP'
(Other definitions for laptop that I've seen before include "Some work on this" , "Aid for businessman" , "device?" , "Type of computer" , "PC" .)