Longman Dictionary of Contemporary English - must

~1 modal verb (negative short form mustn't) 1 (past usually had to) to have to do something because the situation forces you, because of a rule or law, or because you feel that you should  (All passengers must wear seat belts. | You mustn't tell anyone about this - it's a secret. | I don't really want to make the appointment, but I suppose I must. | Under no circumstances must any member of staff socialize with the patients. | Apologize? Must I? It was all her own fault. | I must admit/say etc)  (I must admit, I was surprised when he passed his driving test first time.)  (- compare have3) 2 (past usually must have) used when you are guessing that something is true or that something has happened because there seems to be no other possibility  (Sam must be nearly 90 years old now. | Buying roses? It must be love. | He must have been drunk to say that. | There must have been ten of them, all hiding in my attic.) 3 a) used to suggest that someone does something, especially because you think they will enjoy it very much or you think it is a very good idea  (You must go and see the new Spielberg movie, the special effects are amazing.) b) used when you want to do something and hope to do it soon  (We must come over and try out that new barbecue of yours.) 4 if you must used to tell someone that they are allowed to do something but that you do not approve or agree with it  ("Can I borrow your car, Mum?" "If you must." | if you must do sth)  (If you must smoke, do it outside please.) 5 you must be joking used when you think someone's suggestion is silly or stupid  (-2000 for that old car? You must be joking!) ~2 n 1 a must something that you must do or must have  (Warm clothes are a must in the mountains.) 2 the liquid from which wine is made; grape juice