Monarch once put foot down on female party member? (7)
I believe the answer is:
stephen
'monarch once' is the definition.
(Stephen of Blois, King of England 1135-1154)
'put foot down on female party member?' is the wordplay.
'put foot down' becomes 'step' (as in stepping on something).
'on' means one lot of letters go next to another.
'female party member?' becomes 'hen' (member of a hen party).
'step'+'hen'='STEPHEN'
(Other definitions for stephen that I've seen before include "- Sondheim, composer" , "English king from eleven hundred and thirty five" , "Man" , "Boxing day is St -'s day" , "Old king" .)