• (stressed) IPA: /mʌst/
• (unstressed) IPA: /məs(t)/

must (must; past must)

1. (modal auxiliary, defective) 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.

   You picked one of two, and it wasn't the first: it must have been the second.

2. (modal auxiliary, defective) 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 negative consequence.

   You must arrive in class on time. — the requirement is an imperative

   This door handle must be rotated fully. — the requirement is a directive

   • 1611, The Holy Bible, […] (King James Version), imprinted at London: By Robert Barker, […], OCLC 964384981 ↗, Acts 9:6 ↗:

     Arise, and go into the city, and it shall be told thee what thou must do.

3. (modal auxiliary, defective) said about something that is very likely, probable, or certain to be true

   The children must be asleep by now.

• French: devoir
• German: müssen
• Italian: dovere
• Portuguese: dever
• Russian: (predicative) до́лжен
• Spanish: deber, tener que

• Russian: должно́ быть

must (plural musts)

1. Something that is mandatory or required.

   If you'll be out all day, a map is a must.

• imperative

• no-no

• French: must or obligation
• German: Muss
• Portuguese: dever

must (plural musts)

1. The property of being stale or musty.
2. Something that exhibits the property of being stale or musty.
3. Fruit juice that will ferment or has fermented, usually from grapes.

   • No sweet grape lies hidden here in the shade of its vine-leaves,

     No fermenting must fills and o'erflows the deep vats.

• French: moût or mout
• German: Most
• Italian: mosto
• Portuguese: mosto
• Spanish: mosto

must (musts, present participle musting; past and past participle musted)

1. (transitive) To make musty.
2. (intransitive) To become musty.

must (plural musts)

1. A time during which male elephants exhibit increased levels of sexual activity and aggressiveness (also spelled musth).
   • 1936, George Orwell, Shooting an Elephant, an essay in the magazine New Writing:

     It was not, of course, a wild elephant, but a tame one which had gone ‘must’.

2. An elephant in this sexual and aggressive state.