To mislay something means to put it down somewhere and then forget where you left it. When you mislay your library book, you know it's somewhere in your house, but you can't remember if you left it on the kitchen counter, beside your bed, or in your backpack. When your dad mislays his car keys, he might check his coat pockets, the kitchen table, and the bathroom counter before finding them in the refrigerator (where he accidentally set them while putting away groceries).

Mislay is different from lose. When you lose something, it might be gone forever: you could have left it at the park or dropped it down a storm drain. When you mislay something, you simply put it down without paying attention, and it's still nearby. You just need to retrace your steps or search the usual spots.

The word suggests a temporary problem caused by distraction or forgetfulness, not carelessness about whether you'll see the item again. Mislaid items usually turn up eventually, often in obvious places you checked three times already.