Fool causes obstruction (4)
I believe the answer is:
clot
This clue might be a double definition.
'fool' is the first definition.
(I've seen this before)
'obstruction' is the second definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'causes' acts as a link.
Can you help me to learn more?
(Other definitions for clot that I've seen before include "Foolish person" , "Clumsy person" , "Semi-solid mass -- dunce" , "Stupid person - lump of blood" , "Coagulated blood; twit" .)