GNU Collaborative International Dictionary of English

Found 4 definitions 

  1.       
Must (mŭst), v. i. or auxiliary. [OE. moste, a pret. generally meaning, could, was free to, pres. mot, moot, AS. mōste, pret. mōt, pres.; akin to D. moetan to be obliged, OS. mōtan to be free, to be obliged, OHG. muozan, G. müssen to be obliged, Sw. måste must, Goth. gamōtan to have place, have room, to able; of unknown origin.]
    1. To be obliged; to be necessitated; -- expressing either physical or moral necessity; as, “a man must eat for nourishment; we must submit to the laws.”

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    2. To be morally required; to be necessary or essential to a certain quality, character, end, or result; as, “he must reconsider the matter; he must have been insane.”

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    Likewise must the deacons be grave. 1 Tim. iii. 8.

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    Morover, he [a bishop] must have a good report of them which are without. 1 Tim. iii. 7.

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    ☞ The principal verb, if easily supplied by the mind, was formerly often omitted when must was used; as, “I must away”. “I must to Coventry.” Shak.

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  2.       
Must, n. [AS. must, fr. L. mustum (sc. vinum), from mustus young, new, fresh.  Cf. Mustard.]
    1. The expressed juice of the grape, or other fruit, before fermentation. “These men ben full of must.”  Wyclif (Acts ii. 13.).

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    No fermenting must fills . . . the deep vats. Longfellow.

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    2. [Cf. Musty.] Mustiness.

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  3.       
Must, v. t. & i. To make musty; to become musty.

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  4.       
must, musth (mŭst), a. [Hind. mast intoxicated, ruttish, fr. Skr. matta, p.p. of mad to rejoice, intoxicate.] (Zool.) Being in a condition of dangerous frenzy, usually connected with sexual excitement; -- said of adult male elephants which become so at irregular intervals, typicaly due to increased testosterone levels. -- n.  (a) The condition of frenzy. (b) An elephant in must.

    [Webster 1913 Suppl. +PJC]