must

To do as a requirement; indicates that the sentence subject is required as an imperative or directive to execute the sentence predicate, with failure to do so resulting in a failure or negative consequence.

You must arrive in class on time.

This door handle must be rotated fully.

To do with certainty; indicates that the speaker is certain that the subject will have executed the predicate.

If it has rained all day, it must be very wet outside.

Where would you have put the keyring? You couldn’t have lost it again! - I must have, because it's nowhere to be found.

Used to indicate that something is very likely, probable, or certain to be true.

The children must be asleep by now.

There's the doorbell. It must be Dad.

Something that is mandatory, required or recommended.

If you're trekking all day, a map is a must.

"There are no musts in my life - I'm free, white, and twenty-one."

The property of being stale or musty.

Something that exhibits the property of being stale or musty.

Fruit juice that will ferment or has fermented, usually from grapes.

No sweet grape lies hidden here in the shade of its vine-leaves, No fermenting must fills and o'erflows the deep vats.