Duck down under the bedcover (9)
I believe the answer is:
eiderdown
'the bedcover' is the definition.
(I've seen this before)
'duck down under' is the wordplay.
'duck' becomes 'eider' (eider duck is a kind of duck).
'under' is a charade indicator (letters next to each other).
'eider'+'down'='EIDERDOWN'
(Other definitions for eiderdown that I've seen before include "Find cover" , "What might keep one warm" , "I wondered about this warm bed covering" , "what keeps retired people warm" , "what may be on tonight" .)