To take advantage of someone or something in a presumptuous, unwarranted, or unwelcome manner. I always try to give my students the benefit of the doubt, but those who would presume on my leniency will find themselves facing harsh punishments. I'm your brother, Tim, I want to help you—just don't presume on me, that's all. Thank you for your offer, but I wouldn't want to presume on your hospitality.