must

Old English moste, past tense of motan "have to, be able to," from Proto-Germanic *mot- "ability, leisure (to do something)" (cf. Old Saxon motan "to be obliged to, have to," Old Frisian mota, Middle Low German moten, Dutch moeten, German müssen "to be obliged to," Gothic gamotan "to have room to, to be able to"), perhaps from PIE root *med- "to measure, to take appropriate measures" (see medical (adj.)). Used as present tense from c.1300, from the custom of using past subjunctive as a moderate or polite form of the present.