modal verb

 

necessary used to say that it is necessary that something happens or is done

The meat must be cooked thoroughly.

 

likely used to show that you think something is very likely or certain to be true

It must have been very upsetting for her.

 

suggest used to show that you think it is a good idea for someone to do something

You must come and stay with us some time.

 

noun

 

If something is a must, it is very important to have or do it.

The restaurant has become so popular that reservations are a must.