Longman Dictionary of Contemporary English homepage

Language: Old English
Origin: moste, from motan 'to be allowed to, have to'

must

1 modal verb
     
must1 S1 W1 negative short form mustn't
1 past tense had to to have to do something because it is necessary or important, or because of a law or order [↪ have, 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.
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.
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 joke2 (2)

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