Keen to help out Victor (4)
I believe the answer is:
avid
'keen' is the definition.
(both can mean enthusiastic)
'help out victor' is the wordplay.
'help' becomes 'aid' (synonyms).
'out' is an insertion indicator.
'victor' becomes 'V' (phonetic alphabet: alpha, bravo, charlie etc.).
'aid' placed around 'v' is 'AVID'.
'to' is the link.
(Other definitions for avid that I've seen before include "Impassioned about diva" , "Zealous, enthusiastic" , "In operation" , "Greedy - enthusiastic" , "'Eager, zealous (4)'" .)