Plug hole in motorway certain to produce accident (12)
I believe the answer is:
misadventure
'accident' is the definition.
(I know that accident can be written as misadventure)
'plug hole in motorway certain' is the wordplay.
'plug' becomes 'ad' (as in plugging a product).
'hole' becomes 'vent' (vent is a kind of hole).
'in' means one lot of letters goes inside another.
'motorway' becomes 'MI' (resembles Mv, English motorway).
'certain' becomes 'sure' (synonyms).
'ad'+'vent'='advent'
'mi'+'sure'='misure'
'advent' placed inside 'misure' is 'MISADVENTURE'.
'to produce' acts as a link.
(Other definitions for misadventure that I've seen before include "Bad luck; accidental killing" , "Mishap" , "disaster" , "Unfortunate incident" , "Accident" .)