(1):

(n.) The imperative mood; also, a verb in the imperative mood.

(2):

(a.) Expressive of commund, entreaty, advice, or exhortation; as, the imperative mood.

(3):

(a.) Expressive of command; containing positive command; authoritatively or absolutely directive; commanding; authoritative; as, imperative orders.

(4):

(a.) Not to be avoided or evaded; obligatory; binding; compulsory; as, an imperative duty or order.