Stop learner driver wearing stetson? (4)
I believe the answer is:
halt
'stop' is the definition.
(halting is a kind of stopping)
'learner driver wearing stetson?' is the wordplay.
'learner driver' becomes 'l' (I've seen this in other clues).
'wearing' is an insertion indicator.
'stetson?' becomes 'hat' (stetson is a kind of hat).
'l' going into 'hat' is 'HALT'.
(Other definitions for halt that I've seen before include "limping" , "Stop, small station" , "Falter - stop" , "Stop; minor station" , "Limp; minor station" .)