noun
knife edge
Refers to a very thin, sharp edge like that of a knife. Used in both literal and figurative contexts, such as describing a precarious situation or a sharp dividing line.
その議論はナイフエッジの上を歩くようなものだった。
The debate was like walking on a knife edge.
ナイフエッジの精度が要求される部品だ
It's a part that requires knife-edge precision.