In bed, perhaps, resented and sent out (4)
I believe the answer is:
reed
'in bed' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for reed that I've seen before include "Clarinet part; plant" , "Tall woody grass" , "Tall water-loving grass" , "Rush" , "Grass of marshy land" .)