An Etymological Dictionary of the German Language/müssen
müssen, anom. vb., ‘to be obliged; must,’ from MidHG. müeȥen, OHG. muoȥan, pret. pres., ‘to like, be able; be allowed, be obliged’ (see Muße); comp. OSax. motân, Du. moeten, ‘to be obliged; ought,’ AS. *motan, ‘to be allowed, be able, like, be obliged,’ in E. only the pret. must (AS. môste, ‘was obliged’) has been preserved with the meaning of the pres.; Goth. gamôtan, ‘to take place, have room.’ The origin of these cognates is doubtful; they can scarcely be connected with messen.