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(some place) to sneak or go into a place quietly and unnoticed. I think we can slip in the rear door unnoticed. We slipped in and crept up the stairs.
slip in(to something)
to slide or glide into something, such as clothing, a sleeping bag, a tight place, etc. I don't want to slip into a cold sleeping bag. How can I warm it up? I opened the bag and slipped in.
slip something in (to) somethingand slip something in
to cause something to slide or glide into something. Max slipped the bullets into their chambers and got ready to fire. He slipped the bullets in silently.
1. To insert something gradually, easily, or without being noticed: She took a dollar bill and slipped it in the birthday card. He slipped in a comment during their conversation.
2. To enter gradually, easily, or without being noticed: The party had already started, so I slipped in and got a drink. The thief slipped in the back door.