must
1 Americanauxiliary verb
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to be obliged or bound to by an imperative requirement.
I must keep my word.
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to be under the necessity to; need to.
Animals must eat to live.
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to be required or compelled to, as by the use or threat of force.
You must obey the law.
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to be compelled to in order to fulfill some need or achieve an aim.
We must hurry if we're to arrive on time.
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to be forced to, as by convention or the requirements of honesty.
I must say, that is a lovely hat.
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to be or feel urged to; ought to.
I must buy that book.
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to be reasonably expected to; is bound to.
It must have stopped raining by now. She must be at least 60.
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to be inevitably certain to; be compelled by nature.
Everyone must die.
verb (used without object)
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to be obliged; be compelled.
Do I have to go? I must, I suppose.
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Archaic. (sometimes used with ellipsis of go, get, or some similar verb readily understood from the context).
We must away.
adjective
noun
noun
noun
noun
verb (used with object)
verb
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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
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used as an auxiliary to indicate necessity
I must go to the bank tomorrow
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used as an auxiliary to indicate the probable correctness of a statement
he must be there by now
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used as an auxiliary to indicate inevitability
all good things must come to an end
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on the part of the speaker when used with I or we
I must finish this
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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
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(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
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(foll by away) used with an implied verb of motion to express compelling haste
I must away
noun
noun
noun
noun
combining form
Synonym Usage
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.
Etymology
Origin of must1
First recorded before 900; Middle English most(e), Old English mōste (past tense); cognate with German musste. See mote 2
Origin of must2
First recorded before 900; Middle English, Old English, from Latin mustum, short for vīnum mustum “new wine”
Origin of must3
First recorded in 1595–1605; back formation from musty 1
Origin of must4
First recorded in 1480–90; earlier moist, from Middle French must, variant of musc; see origin at musk
Explanation
A must is something that's so important it can't be missed or ignored. When you're taking kayaking lessons, a lifejacket is a must. Anything that is required is a must: drinking enough water is a must for being healthy. When you adopt a new dog, making sure he'll get along with your cat is a must. Another meaning of the noun must is a stale, stuffy smell. Your damp basement and dry, hot attic might both smell of must. This meaning comes from the adjective musty, a variation on the older, now obsolete moisty.
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
See Examples For:
As a landmark Internal Revenue Service ruling put it, they must be “operated primarily for the purpose of bringing about civic betterments and social improvements.”
From The Wall Street Journal ● Nov. 6, 2026
Sometimes a blade doesn't cool quite as planned, for example two crystals form within it instead of just one, and the metal alloy must be reprocessed so that the manufacturer may re-use the material.
From BBC ● Nov. 6, 2026
While "investments in renewable energy are essential", Turkey's energy transition "must be carried out in a planned and gradual manner," he stressed.
From Barron's ● Nov. 6, 2026
Contenders for the most conservative portfolio, for example, must have a high dividend, strong revenue growth and high margins.
From The Wall Street Journal ● Nov. 6, 2026
Something must have been up if we had only one returning stray and I was still being booted.
From "Legendary Frybread Drive-In" by Cynthia Leitich Smith
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“SailGP to my mind is a must-have, a must- do in terms of competitive racing,” he said.
From Seattle Times ● Oct. 6, 2021
And there are other pieces of must- and should-pass legislation, including extending authority for highway and infrastructure spending, reauthorizing the Export-Import Bank and dealing with various expiring tax provisions.
From New York Times ● Aug. 23, 2015
Michael Frayn’s 1982 farce “Noises Off,” now playing in a new production at the Old Vic, is the latest in a line of must- see comedies.
From BusinessWeek ● Dec. 16, 2011
This must- have publication is still the best basic orientation to the Internet.
From Email 101 by John Goodwin
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