I. must 1 S1 W1 /məst; strong mʌst/ BrE AmE modal verb ( negative short form mustn’t )
[ Language: Old English ; Origin: moste , from motan 'to be allowed to, have to' ]
1 . ( past tense had to ) to have to do something because it is necessary or important, or because of a law or order ⇨ have to , oblige :
All passengers must wear seat belts.
It’s getting late. I really must go.
You must work hard.
We must all be patient.
Must I pay now?
For the engine to work, the green lever must be in the ‘up’ position.
Accidents must be reported to the safety officer.
REGISTER
In everyday English, people usually say someone has to or has got to do something rather than say they must do something , which can sound slightly formal or emphatic:
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Everyone has to wear a seat belt.
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I‘ve got to go at four o’clock.
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Do I have to pay now?
2 . used in negative sentences to say that something should not happen, because of a rule or law or because of the situation:
You mustn’t talk to your mother like that.
This book must not be removed from the library.
We must never forget how much we owe to these brave men.
No one must disturb him while he’s sleeping.
GRAMMAR
Do not use must not to say that it is not necessary for someone to do something. Instead, use need not or do not have to :
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You need not (NOT must not) work through the exercises in order.
3 . used to say you think something is very likely to be true or very likely to have happened:
Sam must be nearly 90 years old now.
His new car must have cost around £20,000.
You must have been really upset.
There must be something wrong with the engine.
Karl must’ve seen ‘Star Wars’ six or seven times.
4 . especially British English spoken used to suggest that someone should do something, especially because you think they will enjoy it or you think it is a good idea:
You must come and stay with us in London sometime.
‘We must do this again,’ he said. ‘I’ve enjoyed it thoroughly.’
5 . especially British English spoken used to say that you intend or want to do something:
I must call her tonight.
6 . I must admit/say/confess spoken used to emphasize what you are saying:
I must say, it gave me quite a shock.
7 . (why) must you ...? spoken used to tell someone that their behaviour upsets or annoys you:
Must you spoil everything?
Why must you always be so suspicious?
8 . a must-have/must-see/must-read etc informal something that is so good, exciting, or interesting that you think people should have it, see it etc:
The exhibit is a must-see for anyone interested in Japanese art.
a must-read novel
9 . if you must (do something) spoken used to tell someone that they are allowed to do something, but that you do not approve of it or agree with it:
All right, come along, if you must.
If you must smoke, please go outside.
10 . if you must know spoken used when you answer a question that you think someone should not have asked, because it is slightly impolite:
Well, if you must know, I’m thirty-six.
⇨ you must be joking at ↑ joke 2 (2)
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THESAURUS
▪ must do something used when saying that it is very important that someone does something, because someone in authority or a rule says this, or because of the situation:
You must be home by midnight.
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He must not smoke in here.
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I must remember to call her.
▪ have to do something to need to do something because it is necessary or important:
I have to go home early.
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She has to talk to him first.
▪ be obliged to do something especially British English to have to do something, because of a legal, professional, or social rule:
Members of parliament are obliged to declare all their financial interests.
▪ be required to do something ( also be obliged to do something especially American English ) formal to have to do something – used especially in written notices and official documents:
New students are required to register with a doctor.
▪ have an obligation to do something ( also be under an obligated to do something ) to have to do something because it is the duty of someone in your position to do it, or because you have officially agreed to do it:
The landlord is under an obligation to keep the building in good repair.
▪ be forced/compelled to do something to have to do something that you do not want to do, because you are in a situation that makes it impossible to avoid:
She was forced to retire early due to ill health.
II. must 2 /mʌst/ BrE AmE noun [countable usually singular]
[ Date: 1800-1900 ; Origin: ⇨ ↑ must 1 ]
something that you must do or must have:
Warm clothes are a must in the mountains.