must (v.) Look up must at Dictionary.com
O.E. moste, pt. of motan "have to, be able to," from P.Gmc. *motanan "to fix, allot, appoint, to have room, to be able" (cf. O.Fris. mota, M.L.G. moten, Du. moeten, Ger. müssen "to be obliged to," Goth. gamotan "to have room to, to be able to"), from PIE base *med- "to measure." Used as present tense from c.1300, from the custom of using past subjunctive as a moderate or polite form of the present. The noun meaning "something that has to be seen or experienced" is from 1892.
must (n1.) Look up must at Dictionary.com
"new wine," O.E. must, from L. mustum, short for vinum mustum "fresh wine," neut. of mustus "fresh, new."
must (n2.) Look up must at Dictionary.com
"mold," c.1600, perhaps a back-formation of musty (q.v.).
must (n3.) Look up must at Dictionary.com
"male elephant frenzy," 1871, from Urdu mast "intoxicated, in rut," from Pers. mast, lit. "intoxicated," related to Skt. matta- "drunk, intoxicated," pp. of madati "boils, bubbles, gets drunk," from PIE base *mad- "wet, to drip."