Powerful weaponry, ominous positioned in middle of major road (9)
I believe the answer is:
artillery
'powerful weaponry' is the definition.
'ominous positioned in middle of major road' is the wordplay.
'ominous' becomes 'ill'.
'positioned in middle of' is an insertion indicator.
'major road' becomes 'artery' (I've seen this before).
'ill' going inside 'artery' is 'ARTILLERY'.
(Other definitions for artillery that I've seen before include "Gunners" , "Army unit that uses big guns" , "Large pieces" , "Powerful guns" , "Guns, cannons etc" .)