It may be on the bed against the window (11)
I believe the answer is:
counterpane
'it may be on the bed' is the definition.
The definition suggests a singular noun which matches the answer. I also know that 'bed' relates to this answer.
'against the window' is the wordplay.
'against' becomes 'counter'.
'the window' becomes 'pane' (I can't justify this - if you can you should give a lot more credence to this answer).
'counter'+'pane'='COUNTERPANE'
Can you help me to learn more?
(Other definitions for counterpane that I've seen before include "retiree's cover" , "Bed cover" , "one goes to bed" , "one lying on the bed?" , "Bedspread" .)