Definition of musts:
(v) :
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.
(v) :
To do with certainty; indicates that the speaker is certain that the subject will have executed the predicate.
(v) :
Used to indicate that something is very likely, probable, or certain to be true.
(n) :
Something that is mandatory, required or recommended.
(n) :
The property of being stale or musty.
(n) :
Something that exhibits the property of being stale or musty.