Fool caught inside hill (5)
I believe the answer is:
dunce
'fool' is the definition.
(both can mean a stupid person)
'caught inside hill' is the wordplay.
'caught' becomes 'c' (cricket abbreviation).
'inside' means one lot of letters goes inside another.
'hill' becomes 'dune' (I have seen 'Hill of sand ' mean 'dune' so perhaps 'hill' could also mean 'dune').
'c' going into 'dune' is 'DUNCE'.
(Other definitions for dunce that I've seen before include "Halfwit" , "Old word for one slow at learning" , "Old word for person slow at learning" , "Poor scholar, slow at learning" , "Poor learner" .)