Cinema shortened Christmas party after reflection (5)
I believe the answer is:
odeon
'cinema' is the definition.
(I've seen this before)
'shortened christmas party after reflection' is the wordplay.
'shortened' means to remove the last letter.
'christmas' becomes 'Noel' (Noel can mean Christmas).
'party' becomes 'do' (do can informally mean a party).
'after reflection' shows that the letters should be reversed in order.
'noel' with its final letter taken away is 'noe'.
'noe'+'do'='noedo'
'noedo' back-to-front is 'ODEON'.
(Other definitions for odeon that I've seen before include "old theatre" , "Ancient Greek concert hall" , "Hal" , "Large UK cinema chain" , "dramas here" .)