The man maintaining I would go to ground (4)
I believe the answer is:
hide
'go to ground' is the definition.
(thesaurus)
'the man maintaining i would' is the wordplay.
'the man' becomes 'he' (**).
'maintaining' means one lot of letters goes inside another.
'i would' becomes 'id'.
'he' placed around 'id' is 'HIDE'.
(Other definitions for hide that I've seen before include "Take cover - skin" , "Keep quiet" , "harbour" , "A flower; an instrument" , "mask" .)