must not

/mʌst nɒt/

strong prohibition

You must not touch that wire; it's live.

The speaker is strongly forbidding someone from touching the wire because it's dangerous.

formalinformal

Used to express a strong prohibition or command that something should not be done under any circumstances.

Students must not cheat on exams.

This rule emphasizes that cheating is strictly forbidden in exams.

You must not leave the house without telling me.

The speaker is insisting that the listener must inform them before leaving.

Often used in rules, regulations, or strong warnings. Can be softened with 'should not' for less strict advice.

Collocations

must not beused to emphasize that something is impossible or forbiddenmust not doused to prohibit an action

contraction of 'must not'

'Must not' is formal and strong, while 'should not' is softer. In casual speech, 'mustn't' is common.

'Must not' is used to enforce rules or express strong disapproval, not just advice.

Derived from the modal verb 'must' (expressing obligation) combined with the negation 'not' to form a strong prohibition.

In formal contexts, 'must not' is stronger than 'should not.' In informal speech, 'mustn't' is often used as a contraction.

must

expresses obligation or necessity

root

not

negates the obligation, creating a prohibition

suffix

English Dictionary