must

The word “must” means used to say that something is required or necessary. In plain terms, expresses obligation ("you must go") or strong likelihood ("that must be true"), or as a noun, something essential.

“Must” is pronounced muhst (/məst/ in IPA).

Here is “must” used in a sentence: “You must show your passport before boarding.”

Depending on how it is used, “must” can be a verb and a noun.

The word “must” comes from Old English. From Old English moste, the past tense of a verb meaning "to be allowed or obliged to.".

“Must” is a very common word in modern English, usually learned at around the A1 level.

“Must” has 3 distinct senses listed in this dictionary. The most common is: used to say that something is required or necessary.

Both express necessity, but "must" often comes from the speaker's own sense of obligation or a strong personal view, as in "I must call her." "Have to" usually points to an outside rule or circumstance, as in "I have to wear a uniform." In everyday speech they overlap, but "must" feels more urgent and personal.

"Must" states that something is necessary or required, with no real choice. "Should" gives advice or a recommendation, leaving room to decide otherwise. "You must stop at a red light" is a rule; "you should rest more" is guidance. Must carries obligation; should carries suggestion, so must is far stronger.

They mean opposite things. "Must not" is a prohibition; it is forbidden, so "you must not walk on the grass" bans it entirely. "Don't have to" means there is no obligation, but you may if you wish, so "you don't have to come" leaves it open. Confusing the two can completely reverse your meaning.

Here "must" does not express obligation but a confident guess, or deduction. Seeing the evidence, the speaker concludes something is almost certainly true, so "he must be tired" means "I'm sure he is tired." This use expresses strong probability based on reasoning, rather than a rule or a requirement to act.