Meaning of “must” in the English Dictionary

"must" in British English

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mustmodal verb

uk strong /mʌst/ weak /məst/ /məs/ us strong /mʌst/ weak /məst/ /məs/

must modal verb (NECESSARY)

A2 used to show that it is necessary or very important that something happens in the present or future:

Meat must be cooked thoroughly.
I must get some sleep.
You mustn't show this letter to anyone else.
Luggage must not be left unattended (= it is against the rules).
formal Must you leave so soon?
formal "Must I sign this?" "Yes, you must."

If you say that you must do something, you mean that you strongly intend to do something in the future:

I must phone my sister.
We must get someone to fix that wheel.
UK I mustn't bite my nails.

used for emphasis:

I must say, you look absolutely great.
I must admit, I wasn't looking forward to it.

B1 If you tell someone else that they must do something pleasant, you are emphasizing that you think it is a good idea to do that:

You must come and stay with us one weekend.
We must meet for lunch soon.

More examples

  • I must do some ironing tonight.
  • Food must be heated to a high temperature to kill harmful bacteria.
  • You must give the bank a written notification if you wish to close your account.
  • Soldiers must obey orders.
  • Candidates must answer two questions from each paper.

must modal verb (PROBABLY)

B2 used to show that something is very likely, probable, or certain to be true:

Harry's been driving all day - he must be tired.
There's no food left - we must have eaten it all.
When you got lost in the forest you must have been very frightened.
"You must know Frank." "No, I don't."

More examples

  • There must be a phone directory in the office somewhere.
  • There's water on the floor - we must have a leak.
  • Try to imagine what life must have been like for Neolithic man 10,000 years ago.
  • The letter must have gone astray in the post.
  • Why am I under arrest? There must be some mistake.

mustnoun [ C ]

uk strong /mʌst/ /məst/ /məs/ us /mʌst/ /məst/ /məs/ informal

must-prefix

uk /mʌst-/ us /mʌst-/ informal

(Definition of “must” from the Cambridge Advanced Learner’s Dictionary & Thesaurus © Cambridge University Press)

"must" in American English

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mustmodal verb

us /mʌst, məst/ must

must modal verb (BE NECESSARY)

used to show that it is necessary or important that something happen in the present or future:

Seeing what others have and she lacks, she believes that she must have more.
We must not surprise them (= it is wrong, dangerous, or forbidden).

If you say that you must do something, you can mean that you have a firm intention to do something in the future:

I must call my sister later.

Must is sometimes used for emphasis:

I must admit I enjoy these movies.

must modal verb (PROBABLY)

used to show that something is likely, probable, or certain to be true:

Death must be better than this.
"It must have been fun." "No, it wasn’t."

mustnoun [ C ]

us /mʌst/

something that is necessary:

If you live in the suburbs a car is a must.

(Definition of “must” from the Cambridge Academic Content Dictionary © Cambridge University Press)

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