Excellent of French to provide assistant (4)
'assistant' is the definition.
(aide is a kind of assistant)
'excellent of french' is the wordplay.
'excellent' becomes 'ai'.
'of french' becomes 'de'.
'to provide' is the link.
(Other definitions for aide that I've seen before include "One to assist", "Adviser or assistant", "Military officer acting as assistant", "a help", "one helping".)