noun
definition
Something that is mandatory or required.
example
If you'll be out all day, a map is a must.
synonyms
verb
definition
(modal auxiliary, defective) To do with certainty; indicates that the speaker is certain that the subject will have executed the predicate.
example
If it has rained all day, it must be very wet outside.
definition
(modal auxiliary, defective) 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 negative consequence.
example
This door handle must be rotated fully.
definition
(modal auxiliary, defective) said about something that is very likely, probable, or certain to be true
example
The children must be asleep by now.