- Historical a warship with cannons on three decks
- any structure with three levels
- Informal a sandwich made with three slices of bread
- Informal a novel published in three volumes; now, esp., any very lengthy novel
- A ship having three decks, especially one of a class of sail-powered warships with guns on three decks.
- Something with three levels or layers, as:a. A three-story apartment building.b. A sandwich having three slices of bread.