Lofty monarch hauling bags (8)
I believe the answer is:
towering
'lofty' is the definition.
('towering' can be a synonym of 'lofty')
'monarch hauling bags' is the wordplay.
'monarch' becomes 'er' (abbreviation for Elizabeth Regina).
'hauling' becomes 'towing'.
'bags' is an insertion indicator (bag can mean secures or steals).
'er' placed into 'towing' is 'TOWERING'.
(Other definitions for towering that I've seen before include "I get worn (anag)" , "Magnificent" , "Grew into (anag.)" , "Very intense (rage)" , "Very tall" .)