means The act of taking something for granted as true before it's proven, or behavior that oversteps what's permitted by being too bold or forward.

from From Latin 'praesumere,' to take beforehand — 'prae-' (before) plus 'sumere' (to take), the same 'sumere' behind 'consume' and 'assume.' It traveled through Old French 'presumption' into English, carrying both its neutral sense (taking a thing for granted) and its prickly one (taking liberties you weren't given). The arrogance shading came along early: to 'take beforehand' easily becomes to take what isn't yet yours.