Road marker from motorway with large English letters (8)
I believe the answer is:
milepost
'road marker' is the definition.
(I've seen this in another clue)
'motorway with large english letters' is the wordplay.
'motorway' becomes 'MI' (resembles Mp, English motorway).
'with' means one lot of letters go next to another.
'large' becomes 'L' (eg in clothes sizes).
'english' becomes 'E' (abbreviation as in OED).
'letters' becomes 'post' (letters in the mail or post).
'mi'+'l'+'e'+'post'='MILEPOST'
'from' acts as a link.
(Other definitions for milepost that I've seen before include "Eight-furlong marker" , "Distance marker" , "measure of progress" .)