be obliged to; should (expressing necessity)

you must show your ID card

the essay mustn't be over 2,000 words

she said she must be going

expressing an opinion about something that is logically very likely

there must be something wrong

you must be tired

something that should not be overlooked or missed

this video is a must for everyone

grape juice before or during fermentation

mustiness, dampness, or mould

a pervasive smell of must

a condition of heightened aggression and unpredictable behaviour occurring annually in certain male animals, especially elephants and camels, in association with a surge in testosterone level, equivalent to the rutting season of deer and some other mammals

a big old bull elephant in must