Bury a test about motorway (10)
I believe the answer is:
interstate
'motorway' is the definition.
(I've seen this before)
'bury a test about' is the wordplay.
'bury' becomes 'inter' (to inter is to put into the ground).
'about' indicates anagramming the letters.
'a'+'test'='atest'
'atest' is an anagram of 'state'.
'inter'+'state'='INTERSTATE'
(Other definitions for interstate that I've seen before include "highway" , "American motorway" , "road in US" , "American way" , "between parts of US" .)