All 5 meanings

1. (auxiliary, infinitive replaces past participle) to be allowed (to do something); to be permitted (to do something); may
2. (intransitive or transitive, past participle as above) to be allowed or permitted to do something implied or previously stated; may
3. (subjunctive II, auxiliary) expresses a prediction with mild doubt, that something is estimated or probable
4. (colloquial) must, to have [got] to, gotta
5. (obsolete, transitive, with genitive) to need, to require