Mountain housing a wind generator (4)
I believe the answer is:
bean
'wind generator' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'mountain housing a' is the wordplay.
'mountain' becomes 'ben' (ben is a kind of mountain).
'housing' is an insertion indicator.
'ben' enclosing 'a' is 'BEAN'.
Can you help me to learn more?
(Other definitions for bean that I've seen before include "Kidney-shaped seed as for coffee" , "Edible seed" , "kept by the counter?" , "Haricot or runner?" , "Pulse" .)