noun
dull sword; blunt sword
Literally a sword that is not sharp. Can also be used figuratively for a slow-witted person or ineffective method, though that usage is less common.
鈍刀では硬いものを切るのは難しい。
It's hard to cut hard things with a dull sword.
彼の議論は鈍刀のように切れ味が悪い。
His argument lacks sharpness, like a blunt sword.