Monarch gets regulation registered (5)
I believe the answer is:
ruler
'monarch' is the definition.
(I've seen this before)
'regulation registered' is the wordplay.
'regulation' becomes 'rule' (synonyms).
'registered' becomes 'R' (abbreviation, as in registered trademark).
'rule'+'r'='RULER'
'gets' acts as a link.
(Other definitions for ruler that I've seen before include "King or, president, say" , "Aid for a straight line" , "Queen, perhaps" , "Measuring stick" , "Person commanding" .)