noun
Refers to a sword that cuts well. Often used figuratively in phrases like 快刀乱麻 (cutting through difficulties decisively).
彼は快刀で竹を一刀両断にした。
He cut the bamboo in two with a single stroke of his sharp sword.
快刀乱麻の決断で問題を解決した。
He solved the problem with a decisive, cutting-through-the-Gordian-knot decision.