Moving regally mostly (7)
I believe the answer is:
largely
'mostly' is the definition.
(I know that mostly can be written as largely)
'moving regally' is the wordplay.
'moving' is an anagram indicator (letters are moved around).
'regally' with letters rearranged gives 'LARGELY'.
(Other definitions for largely that I've seen before include "To a great extent" , "as a rule" , "In the main" , "Mostly found in gallery" , "On the whole" .)