Translation guide
The central stone at the top of an arch, or metaphorically the most important part of something.
The wedge-shaped stone at the crown of an arch that locks the others in place.
The central supporting element of a system, plan, or argument.
Means 'pivot' or 'linchpin'. Commonly used metaphorically for the crucial part of something.
アーチの要石が外れると全体が崩れる。
If the keystone of the arch comes out, the whole thing collapses.
この橋の楔石は特に大きい。
The keystone of this bridge is especially large.
The keystone of this plan is fundraising.
Also used figuratively, like the English 'keystone'.
Education is the keystone of society.
Loanword from English, used in specific contexts like 'keystone species' or business jargon.
Protection of keystone species is important.