A very slip, petite person or thing. (Most often completed by "girl," "boy," or "thing.") You wouldn't think it to look at me know, but I was just a slip of a boy growing up. No one suspected that the tiny slip of a girl roaming the square was pickpocketing ever tourist she passed. A: "Wow, you got a short story published?" B: "It's just a slip of a thing, but I'm pretty pleased all the same."