Merriam-Webster Collegiate Dictionary - must

 I. verb  (present & past all persons ~)  Etymology: Middle English moste, from Old English moste, past indicative & subjunctive of motan to be allowed to, have to; akin to Old High German muozan to be allowed to, have to  Date: before 12th century  verbal auxiliary  1.  a. be commanded or requested to you ~ stop  b. be urged to ; ought by all means to you ~ read that book  2. be compelled by physical necessity to one ~ eat to live ; be required by immediate or future need or purpose to we ~ hurry to catch the bus  3.  a. be obliged to ; be compelled by social considerations to I ~ say you're looking well  b. be required by law, custom, or moral conscience to we ~ obey the rules  c. be determined to if you ~ go at least wait for me  d. be unreasonably or perversely compelled to why ~ you argue  4. be logically inferred or supposed to it ~ be time  5. be compelled by fate or by natural law to what ~ be will be  6. was or were presumably certain to ; was or were bound to if he did it she ~ have known  7. dialect may, shall — used chiefly in questions  intransitive verb archaic to be obliged to go I ~ to Coventry — Shakespeare  II. noun  Date: 1616  1. an imperative need or duty ; requirement  2. an indispensable item ; essential exercise is a ~  III. noun  Etymology: Middle English, from Old English, from Latin ~um  Date: before 12th century the expressed juice of fruit and especially grapes before and during fermentation; also the pulp and skins of the crushed grapes  IV. noun  Etymology: Middle English (Scots) moist, from Middle French ~, alteration of musc musk  Date: 15th century  1. musk  2. mold, ~iness