One stops weapon test to do with bearings (8)
I believe the answer is:
armorial
'to do with bearings' is the definition.
(term in heraldry)
'one stops weapon test' is the wordplay.
'one' becomes 'I' (Roman numeral).
'stops' means one lot of letters goes inside another.
'weapon' becomes 'arm' (synonyms).
'test' becomes 'oral' (oral is a type of examination).
'arm'+'oral'='armoral'
'i' placed into 'armoral' is 'ARMORIAL'.
(Other definitions for armorial that I've seen before include "Relating to heraldry or heraldic arms" , "Sort of bearing" .)