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auxiliary verb
  1. to be obliged or bound to by an imperative requirement: I must keep my word.
  2. to be under the necessity to; need to: Animals must eat to live.
  3. to be required or compelled to, as by the use or threat of force: You must obey the law.
  4. to be compelled to in order to fulfill some need or achieve an aim: We must hurry if we're to arrive on time.
  5. to be forced to, as by convention or the requirements of honesty: I must say, that is a lovely hat.
  6. to be or feel urged to; ought to: I must buy that book.
  7. to be reasonably expected to; is bound to: It must have stopped raining by now. She must be at least 60.
  8. to be inevitably certain to; be compelled by nature: Everyone must die.
verb (used without object)
  1. to be obliged; be compelled: Do I have to go? I must, I suppose.
  2. Archaic. (sometimes used with ellipsis of go, get, or some similar verb readily understood from the context): We must away.
  1. necessary; vital: A raincoat is must clothing in this area.
  1. something necessary, vital, or required: This law is a must.

Origin of must1

before 900; Middle English most(e), Old English mōste (past tense); cognate with German musste. See mote2


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1. Must, ought, should express necessity or duty. Must expresses necessity or compulsion: I must attend to those patients first. Soldiers must obey orders. Ought (weaker than must ) expresses obligation, duty, desirability: You ought to tell your mother. Should expresses obligation, expectation, or probability: You are not behaving as you should. Children should be taught to speak the truth. They should arrive at one o'clock.


  1. new wine; the unfermented juice as pressed from the grape or other fruit.

Origin of must2

before 900; Middle English, Old English < Latin mustum, short for vīnum mustum new wine


  1. mold; moldiness; mustiness: a castle harboring the must of centuries.

Origin of must3

First recorded in 1595–1605; back formation from musty1


  1. musth.


  1. musk, especially a powder made from musk.
verb (used with object)
  1. to powder (the hair).

Origin of must5

1480–90; earlier moist < Middle French must, variant of musc musk


or must

  1. a state or condition of violent, destructive frenzy occurring with the rutting season in male elephants, accompanied by the exudation of an oily substance from glands between the eyes and mouth.

Origin of musth

1870–75; < Urdu mast < Persian: literally, drunk
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for must


verb (takes an infinitive without to or an implied infinitive)
  1. used as an auxiliary to express obligation or compulsion: you must pay your dues . In this sense, must does not form a negative. If used with a negative infinitive it indicates obligatory prohibition
  2. used as an auxiliary to indicate necessityI must go to the bank tomorrow
  3. used as an auxiliary to indicate the probable correctness of a statementhe must be there by now
  4. used as an auxiliary to indicate inevitabilityall good things must come to an end
  5. (used as an auxiliary to express resolution)
    1. on the part of the speaker when used with I or weI must finish this
    2. on the part of another or others as imputed to them by the speaker, when used with you, he, she, they, etclet him get drunk if he must
  6. (used emphatically) used as an auxiliary to express conviction or certainty on the part of the speakerhe must have reached the town by now, surely; you must be joking
  7. (foll by away) used with an implied verb of motion to express compelling hasteI must away
  1. an essential or necessary thingstrong shoes are a must for hill walking

Word Origin

Old English mōste past tense of mōtan to be allowed, be obliged to; related to Old Saxon mōtan, Old High German muozan, German müssen


  1. mustiness or mould

Word Origin

C17: back formation from musty


  1. the newly pressed juice of grapes or other fruit ready for fermentation

Word Origin

Old English, from Latin mustum new wine, must, from mustus (adj) newborn


  1. a variant spelling of musth



  1. (often preceded by in) a state of frenzied sexual excitement in the males of certain large mammals, esp elephants, associated with discharge from a gland between the ear and eye

Word Origin

C19: from Urdu mast, from Persian: drunk
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for must


Old English moste, past tense of motan "have to, be able to," from Proto-Germanic *mot- "ability, leisure (to do something)" (cf. Old Saxon motan "to be obliged to, have to," Old Frisian mota, Middle Low German moten, Dutch moeten, German müssen "to be obliged to," Gothic gamotan "to have room to, to be able to"), perhaps from PIE root *med- "to measure, to take appropriate measures" (see medical (adj.)). Used as present tense from c.1300, from the custom of using past subjunctive as a moderate or polite form of the present.


"new wine," Old English must, from Latin mustum (also source of Old High German, German most, Old French moust, Modern French moût, Spanish, Italian mosto), short for vinum mustum "fresh wine," neuter of mustus "fresh, new, newborn," perhaps literally "wet," and from PIE *mus-to-, from root *meus- "damp" (see moss).


"mold," c.1600, perhaps a back-formation of musty (q.v.).


"male elephant frenzy," 1871, from Urdu mast "intoxicated, in rut," from Persian mast, literally "intoxicated," related to Sanskrit matta- "drunk, intoxicated," past participle of madati "boils, bubbles, gets drunk," from PIE root *mad- "wet, moist" (see mast (n.2)).


"that which has to be done, seen, or experienced," 1892, from must (v.). As an adjective, "obligatory, indispensable," by 1912, from the noun; must-read is from 1959.

Online Etymology Dictionary, © 2010 Douglas Harper

must in Science


  1. An annual period of heightened aggressiveness and sexual activity in male elephants.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Idioms and Phrases with must


The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.

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