adj. & n.
adj. 1 requiring to be done, achieved, etc.; requisite, essential (it is necessary to work; lacks the necessary documents). 2 determined, existing, or happening by natural laws, predestination, etc., not by free will; inevitable (a necessary evil). 3 Philos. (of a concept or a mental process) inevitably resulting from or produced by the nature of things etc., so that the contrary is impossible. 4 Philos. (of an agent) having no independent volition.
n. (pl. -ies) (usu. in pl.) any of the basic requirements of life, such as food, warmth, etc. the necessary colloq. 1 money. 2 an action, item, etc., needed for a purpose (they will do the necessary).
[ ME f. OF necessaire f. L necessarius f. necesse needful ]