noun: an assumption that is taken for granted
When Mr. Baker found out the family car was gone, he acted under the presumption that his rebellious son had taken the car, calling his son's phone and yelling at him; only later did Mr. Baker realize that Mrs. Baker had simply gone out to get her nails done.
noun: audacious (even arrogant) behavior that you have no right to
The new neighbor quickly gained a reputation for her presumption; she had invited herself to several neighbors' homes, often stopping over at inopportune times and asking for a drink.