assume (v.) Look up assume at Dictionary.com
early 15c., assumpten "to receive up into heaven" (especially of the Virgin Mary), also assumen "to arrogate," from Latin assumere, adsumere "to take up, take to oneself, take besides, obtain in addition," from ad- "to, up" (see ad-) + sumere "to take," from sub "under" (see sub-) + 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.