Upset routine, holding party in royal house (5)
I believe the answer is:
tudor
'royal house' is the definition.
(Tudor is an example)
'upset routine holding party' is the wordplay.
'upset' says the letters should be written in reverse.
'routine' becomes 'rut' (being stuck in a rut is being stuck in a routine).
'holding' indicates putting letters inside.
'party' becomes 'do' (do is a kind of party).
'rut' backwards is 'tur'.
'tur' enclosing 'do' is 'TUDOR'.
'in' acts as a link.
(Other definitions for tudor that I've seen before include "(Pertaining to) royal house" , "A royal house of England" , "Welsh royal family" , "regal dynasty" , "Owen's house" .)