Oddly adorn Turk on highway (5,4)
I believe the answer is:
trunk road
'highway' is the definition.
(trunk road is a kind of highway)
'oddly adorn turk on' is the wordplay.
'oddly' indicates an anagram.
'on' says to put letters next to each other.
'adorn' after 'turk' is 'turkadorn'.
'turkadorn' is an anagram of 'TRUNK-ROAD'.
(Other definitions for trunk road that I've seen before include "Arterial thoroughfare" , "major way" .)