must1 / məst/ • modal verb (past had to or in reported speech must) 1. be obliged to; should (expressing necessity): you must show your ID card it must not be over 2,000 words she said she must be going. ∎ expressing insistence: you must try some of this fish if you must smoke, you could at least go in the living room. ∎ used in ironic questions expressing irritation: must you look so utterly suburban?2. expressing an opinion about something that is logically very likely: there must be something wrong you must be tired.• n. inf. something that should not be overlooked or missed: this video is a must for parents.PHRASES: I must saysee say.must needs do somethingsee needs.must2 • n. grape juice before or during fermentation.must3 • n. mustiness, dampness, or mold: a pervasive smell of must.must4 (also musth) • n. the frenzied state of certain male animals, esp. elephants or camels, that is associated with the rutting season: a big old bull elephant in must.• adj. (of a male elephant or camel) in such a state.