Dope left in bed (4)
I believe the answer is:
clot
'dope' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'left in bed' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in' is an insertion indicator.
'bed' becomes 'cot' (cot is a type of bed).
'l' going into 'cot' is 'CLOT'.
Can you help me to learn more?
(Other definitions for clot that I've seen before include "(Of blood) coagulate" , "Coagulate -- 1 across person" , "Fool - congeal" , "medical problem" , "Idiot - liquid turned to a solid state" .)