must've

Verb

must (third-person singular simple present must, no present participle, simple past must, no past participle)

1. (auxiliary, defective, modal, no-past-participle, no-present-participle) 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.
2. (auxiliary, defective, modal, no-past-participle, no-present-participle) 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.
3. (auxiliary, defective, modal, no-past-participle, no-present-participle) Used to indicate that something is very likely, probable, or certain to be true.
   • The children must be asleep by now.

See all 9 meanings of must