Newly-wed given key to chamber? (5)
I believe the answer is:
groom
'newly-wed' is the definition.
(man who's just got married)
'given key to chamber?' is the wordplay.
'given' means one lot of letters go next to another.
'key' becomes 'g' (musical key).
'to chamber?' becomes 'room' (chamber is a kind of room).
'g' put next to 'room' is 'GROOM'.
(Other definitions for groom that I've seen before include "Prepare for role" , "He's about to be married - tidy him up" , "Tender of horses" , "Bride's choice" , "Officer of Royal Household" .)