A somewhat formal or literary word for something indispensable or of the utmost importance. Often used in written contexts or formal speech.
This plan lacks an essential element.
Safety measures are vital.
Standard kanji form; the only written form.
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.