Webster's English Dictionary

must

1. must \m*s(t), 'm*st\ vb or must [ME moste, fr. OE mo-ste, past indic. & 
   subj. of mo-tan] pres & past all persons  to be allowed to, have to; akin 
   to OHG muozan to be allowed to, have to; akin to OHG muozan to be allowed 
   to, have to, OE metan to measure - more at METE 1a: is commanded or 
   requested to {you ~ stop}  1b: is urged to : ought by all means to {you ~ 
   read that book}  2: is compelled by physical necessity to {man ~ eat to 
   live} :  is required by immediate or future need or purpose to {we ~ hurry 
   if we want to catch the bus} 3a: is obliged to : is compelled by social 
   considerations to {I ~R say you're looking much better} 3b: is required by 
   law, custom, or moral conscience to {we ~ obey  the rules} 3c: is 
   determined to {if you ~ go at least wait till the storm is  over} 3d: is 
   unreasonably or perversely compelled to {why ~ you be so st ubborn} 4: is 
   logically inferred or supposed to {what ~ be will be}  6: was presumably 
   certain to : was bound to {if he had really been the re I ~ have seen him} 
   dial  7: MAY, SHALL - used chiefly in questions  archaic  : ought to go : 
   is obliged to go {I ~ to Coventry -Shak.} 
2. must \'m*st\ n often attrib  1: an imperative need or duty : REQUIREMENT 
    2: an indispensable item : ESSENTIAL 
3. must n [ME, fr. OE, fr. L mustum] : the expressed juice of grapes or 
   other fruit before and during fermentat ion
4. must n [MF, alter. of musc musk] 1: MUSK  2: MUSTINESS, MOLD