From Latin 'necessārius' (unavoidable), from 'necesse' (inevitable), likely from 'ne-' (not) + 'cēdere' (to yield) — something that does not give way.
Required to be done, achieved, or present; needed; essential.
From Latin necessarius (unavoidable, indispensable, requisite), from necesse (unavoidable, essential), a compound of ne- (not) and cedere (to yield, to go, to withdraw) via a form cesse. The root cedere traces to PIE *ked- (to go, to yield), giving English cede, concede, precede, and accede. The original Latin sense of necesse was something that does not yield — an immovable necessity, a thing that cannot be stepped
The word 'necessary' is one of the most commonly misspelled words in English — the stumbling block is whether it has one 's' or two, and one 'c' or two. The mnemonic 'a shirt has one Collar and two Sleeves' matches the pattern: one 'c,' two 's's. Etymologically, the word means 'unyielding' — from Latin 'ne-' (not