Male monarchs (5)
I believe the answer is:
kings
'male monarchs' is the definition.
('king' can be a synonym of 'male monarch')
This is all the clue.
(Other definitions for kings that I've seen before include "Name of two Old Testament books" , "Leaders" , "Valley of the - -" , "College etc of royal foundation" , "Henry James, or Edward Lear?" .)