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

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

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. Unabridged


2 [muhst]
new wine; the unfermented juice as pressed from the grape or other fruit.

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


3 [muhst]
mold; moldiness; mustiness: a castle harboring the must of centuries.

1595–1605; back formation from musty1


4 [muhst]


5 [muhst] Obsolete.
musk, especially a powder made from musk.
verb (used with object)
to powder (the hair).

1480–90; earlier moist < Middle French must, variant of musc musk Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
must1 (mʌst, (unstressed) məst, məs)
vb (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 necessity: I must go to the bank tomorrow
3.  used as an auxiliary to indicate the probable correctness of a statement: he must be there by now
4.  used as an auxiliary to indicate inevitability: all good things must come to an end
5.  used as an auxiliary to express resolution
 a.  on the part of the speaker when used with I or we: I must finish this
 b.  on the part of another or others as imputed to them by the speaker, when used with you, he, she, they, etc: let him get drunk if he must
6.  ( used emphatically ) used as an auxiliary to express conviction or certainty on the part of the speaker: he 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 haste: I must away
8.  an essential or necessary thing: strong shoes are a must for hill walking
[Old English mōste past tense of mōtan to be allowed, be obliged to; related to Old Saxon mōtan, Old High German muozan, German müssen]

must2 (mʌst)
the newly pressed juice of grapes or other fruit ready for fermentation
[Old English, from Latin mustum new wine, must, from mustus (adj) newborn]

must3 (mʌst)
mustiness or mould
[C17: back formation from musty]

must4 (mʌst)
a variant spelling of musth

musth or must (mʌst)
(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
[C19: from Urdu mast, from Persian: drunk]
must or must
[C19: from Urdu mast, from Persian: drunk]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Word Origin & History

O.E. moste, pt. of motan "have to, be able to," from P.Gmc. *motanan "to fix, allot, appoint, to have room, to be able" (cf. O.Fris. mota, M.L.G. moten, Du. moeten, Ger. müssen "to be obliged to," Goth. gamotan "to have room to, to be able to"), from PIE base *med- "to measure." Used as present
tense from c.1300, from the custom of using past subjunctive as a moderate or polite form of the present. The noun meaning "something that has to be seen or experienced" is from 1892.

"new wine," O.E. must, from L. mustum, short for vinum mustum "fresh wine," neut. of mustus "fresh, new."

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

"male elephant frenzy," 1871, from Urdu mast "intoxicated, in rut," from Pers. mast, lit. "intoxicated," related to Skt. matta- "drunk, intoxicated," pp. of madati "boils, bubbles, gets drunk," from PIE base *mad- "wet, to drip."
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
musth also must   (mŭst)  Pronunciation Key 
An annual period of heightened aggressiveness and sexual activity in male elephants.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Idioms & Phrases


see a must; show must go on.

The American Heritage® Dictionary of Idioms by Christine Ammer.
Copyright © 1997. Published by Houghton Mifflin.
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Example sentences
Instructor must have ability to teach in the university's general education
But now it has almost caught up with the developed world it must change its
Some also suggest that to be invasive, a species must have negative effects on
  native wildlife.
And the wide-open landscape looks much as it must have in the state's early
  ranching days.
Idioms & Phrases
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