Own up to hiding millions in part of mine (5)
I believe the answer is:
admit
'own up to' is the definition.
(I've seen this in another clue)
'millions in part of mine' is the wordplay.
'millions' becomes 'm' (abbreviation).
'in' indicates putting letters inside.
'part of mine' becomes 'adit' ('adit' is part of 'mine').
'm' inserted inside 'adit' is 'ADMIT'.
'hiding' is the link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for admit that I've seen before include "Profess" , "Confess; allow in" , "Accept" , "Provide student with place" , "Grant entry to" .)