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.
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.
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
used as an auxiliary to indicate necessity
I must go to the bank tomorrow
used as an auxiliary to indicate the probable correctness of a statement
he must be there by now
used as an auxiliary to indicate inevitability
all good things must come to an end
on the part of the speaker when used with I or we
I must finish this
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
(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
(foll by away) used with an implied verb of motion to express compelling haste
I must away
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.
First recorded before 900; Middle English most(e), Old English mōste (past tense); cognate with German musste. See mote 2
First recorded before 900; Middle English, Old English, from Latin mustum, short for vīnum mustum “new wine”
First recorded in 1595–1605; back formation from musty 1
First recorded in 1480–90; earlier moist, from Middle French must, variant of musc; see origin at musk
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.
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
"It's OK to be a Democrat and be religious," she told AFP, while emphasizing that government must be secular.
From Barron's • Jul. 12, 2026
At its most extreme and troubling end, some believe they must stop an AI apocalypse by any means necessary.
From The Wall Street Journal • Jul. 12, 2026
By law, the money must be invested in a low-cost index fund designed for long-term growth.
From BBC • Jul. 11, 2026
That makes the method especially useful when the original properties of nanoparticles must remain unchanged.
From Science Daily • Jul. 11, 2026
“And I am sure of it, my dear. But we must have the doctor’s verdict too.”
From "The Hiding Place" by Corrie ten Boom
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
