How Well Do You Know English Slang?
early 15c., assumpten "to receive up into heaven" (especially of the Virgin Mary), also assumen "to arrogate," from Latin assumere "to take up, take to oneself," from ad- "to, up" (see ad-) + sumere "to take," from sub "under" + emere "to take" (see exempt (adj.)).
Meaning "to suppose, to take for granted as the basis of argument" is first recorded 1590s; that of "to take or put on (an appearance, etc.)" is from c.1600. Related: Assumed; assuming. Early past participle was assumpt. In rhetorical usage, assume expresses what the assumer postulates, often as a confessed hypothesis; presume expresses what the presumer really believes.