Smithereens means tiny fragments or pieces, especially after something has been violently broken or destroyed. When a baseball crashes through a window and shatters the glass into countless tiny shards, the window has been smashed to smithereens. When a demolition crew uses explosives to destroy an old building, it might blow to smithereens in a cloud of dust and rubble.

The word always appears with “to” or “into”: something is blown to smithereens, smashed to smithereens, or broken into smithereens. You wouldn't say you found “a smithereen” on the ground, though that would be grammatically logical. The word only works in its plural form, probably because when something breaks into smithereens, it breaks into so many pieces that you couldn't possibly count them all.

The word has a satisfying, almost playful sound that makes it fun to say, even though it describes destruction. If your little brother builds an elaborate tower of blocks and your dog's wagging tail knocks it to smithereens, the word captures both the completeness of the destruction and somehow makes the disaster feel a little less serious. When something is in smithereens, there's no putting it back together: it's thoroughly, completely, and perhaps even spectacularly destroyed.