English monarch entertaining MP or Roman ruler (7)
I believe the answer is:
emperor
'roman ruler' is the definition.
(I've seen this in another clue)
'english monarch entertaining mp or' is the wordplay.
'english' becomes 'e' (abbreviation).
'monarch' becomes 'ER' (abbreviation for Elizabeth Regina, British Queen).
'entertaining' is an insertion indicator.
'e'+'er'='eer'
'eer' enclosing 'mp' is 'emper'.
'emper'+'or'='EMPEROR'
(Other definitions for emperor that I've seen before include "Eg, Caesar" , "Male ruler of a group of countries" , "Ancient Roman ruler" , "He rules over several states" , "Supreme ruler" .)