Right to interrupt sleep? Rubbish (5)
I believe the answer is:
dross
'rubbish' is the definition.
(I've seen this before)
'right to interrupt sleep?' is the wordplay.
'right' becomes 'R' (common abbreviation).
'to interrupt' means one lot of letters goes inside another.
'sleep?' becomes 'doss' (I've seen this before).
'r' inserted within 'doss' is 'DROSS'.
(Other definitions for dross that I've seen before include "Waste coal - rubbish" , "Scum on molten metals" , "Scum on molten metal" , "Refuse - dregs" , "Anything worthless" .)