Crossword Genius

Onetime threat to a castle's walls (8)

Ross

I believe the answer is:

catapult

(Other definitions for catapult that I've seen before include "Ancient war machine" , "Stone thrower" , "Y-shaped weapon associated with naughty boys" , "Launch" , "Weapon for hurling stones" .)

I've seen this clue in The New York Times.
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