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English definition of “must”

must

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

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. I mustn't bite my nails. used for emphasis: I must say, you're looking extremely well. 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 for the weekend. We must meet for lunch soon.

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."

must

noun [C] uk   strong /mʌst/ weak /məst/ /məs/ informal us  
something that is necessary: If you live in the country a car is a must.
(Definition of must modal verb, noun from the Cambridge Advanced Learners Dictionary & Thesaurus © Cambridge University Press)
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