something that it is essential to see, do, hear etc; (used to express an obligation or an order)
necessity, essential
the state, condition (e.g. a law of nature, a (serious) need, a social rule etc) that makes a certain result unavoidable; something that one cannot be, live etc without
need, essentiality
(used to tell a person about a present or past duty or obligation) (used to express an opinion, give advice etc about the present or past)
necessity, essential
(something) that is necessary
need