In part, he'll do (5)
I believe the answer is:
actor
'in part' is the definition.
'actor' can be an answer for 'part' (thesaurus). I'm not sure about the 'in' bit.
'he'll do' is the wordplay.
I cannot really see how this works, but
'do' could be 'act' (I've seen this before) and 'act' is located in the answer.
The remaining letters 'or' is a valid word which might be clued in a way I don't see.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for actor that I've seen before include "Person performing on stage or screen" , "One in a play" , "For example, Colman" , "Theatrical performer" , "Stage-player" .)