Holiday of a newly married couple (9)
I believe the answer is:
honeymoon
'holiday of a newly married couple' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for honeymoon that I've seen before include "Sequel to marriage" , "Newlyweds' holiday" , "Holiday just for two?" , "Holiday of a newly married couple" , "First holiday after marriage" .)