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edge (of a knife or sword); blade
prong (of an electrical plug)
この包丁の刃は非常に鋭くて扱いには注意が必要だ。
The blade of this knife is very sharp and requires careful handling.
刃を研ぐと切れ味が格段に良くなるのを実感した。
I really felt the sharpness improved dramatically when sharpening the blade.
古い刀の刃には歴史の重みが感じられるものだ。
You can feel the weight of history in the blade of an old sword.