Entering fashionable thoroughfare, stole motor (7)
I believe the answer is:
inboard
'motor' is the definition.
(an inboard is a boat's engine)
'entering fashionable thoroughfare stole' is the wordplay.
'entering' is an insertion indicator.
'fashionable' becomes 'in' (in can mean fashionable or trendy).
'thoroughfare' becomes 'rd' (abbreviation for road).
'stole' becomes 'boa' (both can mean a type of scarf).
'in'+'rd'='inrd'
'inrd' going around 'boa' is 'INBOARD'.
(Other definitions for inboard that I've seen before include "This motor is located within a boat" , "Within the hull of a ship or boat" , "Within a ship or aircraft" , "housed in Hull?" , "description of boat's engine" .)