Stop enclosing area for engine driver (5)
I believe the answer is:
steam
'for engine driver' is the definition.
(a steam engine is powered by steam)
'stop enclosing area' is the wordplay.
'stop' becomes 'stem' (stem can mean to stop or interrupt).
'enclosing' is an insertion indicator.
'area' becomes 'a' (maths abbreviation).
'stem' placed around 'a' is 'STEAM'.
(Other definitions for steam that I've seen before include "Form of water" , "Momentum - boiled water" , "Vaporised water" , "Hot water vapour" , "Travel in liner" .)