Unrestrained Queen in charge (4)
I believe the answer is:
free
'unrestrained' is the definition.
('free' is associated in meaning with 'unrestrained')
'queen in charge' is the wordplay.
'queen' becomes 'r' (r is abbreviation regina. e.g. in ER ).
'in' means one lot of letters goes inside another.
'charge' becomes 'fee' (fee is a kind of charge**).
'r' inserted within 'fee' is 'FREE'.
(Other definitions for free that I've seen before include "Release; without cost" , "Out of bondage" , "unlike battery hens" , "As cheap as can be!" , "On the house" .)