Meaning of MUST in English

[must] vb, pres & past all persons must [ME moste, fr. OE moste, past indic. & subj. of motan to be allowed to, have to; akin to OHG muozan to be allowed to, have to] verbal auxiliary (bef. 12c) 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 "man ~ 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 be so stubborn"

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 really was there I ~ have seen him"

7. dial: may, shall--used chiefly in questions ~ vi, archaic: to be obliged to go "I ~ to Coventry --Shak."

[2]must n (1616) 1: an imperative need or duty: requirement

2: an indispensable item: essential "exercise is a ~" [3]must n [ME, fr. OE, fr. L mustum] (bef. 12c): the expressed juice of fruit and esp. grapes before and during fermentation; also: the pulp and skins of the crushed grapes [4]must n [ME (Sc) moist, fr. MF must, alter. of musc musk] (15c) 1: musk

2: mold, mustiness

Merriam-Webster English vocab.      Английский словарь Merriam Webster.