presumption (n.)

mid-13c., presumpcioun, "seizure and occupation without right," also "taking upon oneself more than good sense and propriety warrant," from Old French presumcion (12c., Modern French présomption) and directly from Late Latin praesumptionem (nominative praesumptio) "confidence, audacity," in classical Latin, "a taking for granted, anticipation," noun of action from past-participle stem of praesumere "to take beforehand," from prae "before" (see pre-) + sumere "to take, obtain, buy," from sus‑, variant of sub‑ "up from under" + emere "to take" (from PIE root *em- "to take, distribute").

In English, the meaning "the taking of something for granted" is attested from c. 1300; that of "a ground for presuming or believing" is from 1580s. Presumptuous preserves the older sense.