imperative

Definitions:

That form of the verb which expresses command, exhortation, & c.
- Nuttall's Standard dictionary of the English language. By Nuttall, P.Austin. Published 1914. (noun) (n.) (noun)
Expressing command; not to be avoided; as, an imperative necessity; in grammar, expressing command, entreaty, or exhortation; as, the imperative mood.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (adjective) (adj.) (adjective)
Commanding; authoritative; obligatory.
- The Clarendon dictionary. By William Hand Browne, Samuel Stehman Haldeman. Published 1894. (adjective) (adj.) (adjective)
Expressing or containing positive command or desire; positive; authoritative; in gram., the simple form of the verb which expresses command or exhortation, as go, eat, sing.
- Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874. (adjective) (adj.) (adjective)
Expressive of command: authoritative: obligatory.
- The american dictionary of the english language. By Daniel Lyons. Published 1899. (adjective) (adj.) (adjective)
Imperatively.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (adverb) (adv.) (adverb)
Something, as an act or word, that gives or expresses a command; the imperative mood.
- The Winston Simplified Dictionary. By William Dodge Lewis, Edgar Arthur Singer. Published 1919. (noun) (n.) (noun)
Authoritatively commanding.
- Nuttall's Standard dictionary of the English language. By Nuttall, P.Austin. Published 1914. (adjective) (adj.) (adjective)

Usage examples:

Mrs. Kenton was imperative in her alarm.
- Entire PG Edition of The Works of William Dean Howells by William Dean Howells
At last, quite suddenly, came the imperative summons to go out at once to be with Fay when the new baby should arrive.
- Jan and Her Job by L. Allen Harker
Besides, 'tis imperative that I have a private secretary.
- Calvert of Strathore by Carter Goodloe