na-adjective, noun
A somewhat formal or literary word for something indispensable or of the utmost importance. Often used in written contexts or formal speech.
この計画には切要な要素が欠けている。
This plan lacks an essential element.
安全対策は切要である。
Safety measures are vital.
Composed of 切 (せつ, 'urgent, keen') and 要 (よう, 'essential, pivotal'). The combination yields a meaning of 'extremely important' or 'indispensable'. The exact historical derivation is uncertain, but the kanji components directly reflect the word's meaning.