1. To slide down and cover something in an accidental or uncontrollable manner. The bandana kept slipping over my eyes throughout the game. The giant slug slipped over the edge of the bucket and down into the pool of rainwater.
2. To move across the edge of something and fall down to the other side in a quick, smooth motion. The diver secured his equipment and slipped over the side of the boat. I'll just slip over the fence and ask the neighbors if they have any sugar.
3. To move something across the edge or top of something in a quick, effortless, often inconspicuous manner. In this usage, a noun or pronoun is used between "slip" and "over." I slipped the document over the side of the desk so the boss wouldn't see what I was working on. She slipped the briefcase over the counter and the man carried it away without saying a word.
4. To cover someone or something with something else in a quick, smooth motion. In this usage, a noun or pronoun is used between "slip" and "over." Animal control slipped a muzzle over the bear's snout. The kidnappers slipped a black bag over the victim's head and threw him into the back of their van.
5. To come (to some place) very quickly or in a sneaky manner. I'm supposed to be studying, but I'll try slipping over once my parents are asleep. I need to slip over to the office to gather up anything incriminating before the feds arrive.
slip something over someone or something
to cause something to slide or glide over and onto someone or something. Mother slipped the covers over Timmy and kissed him good night. Jane slipped the cover over the birdcage for the night.