Beetle across motorway, then cut corner (7)
I believe the answer is:
chamfer
'cut corner' is the definition.
(I've seen this before)
'beetle across motorway then' is the wordplay.
'beetle' becomes 'chafer' (I've seen this before).
'across' indicates putting letters inside.
'motorway then' becomes 'm' (I can't explain this - if you can you should give a lot more credence to this answer).
'chafer' enclosing 'm' is 'CHAMFER'.
Can you help me to learn more?
(Other definitions for chamfer that I've seen before include "Bevel" , "A pared-off edge" , "Cut corners" , "cut corner" , "Form a bevelled edge on timber etc" .)