1. three-decker(n = noun.food) club sandwich, triple-decker - made with three slices of usually toasted bread;
is a kind of sandwich
2. three-decker(n = noun.artifact) - any ship having three decks;
is a kind of ship
3. three-decker(n = noun.artifact) - a warship carrying guns on three decks;
is a kind of combat ship, war vessel, warship
A vessel of war carrying guns on three decks. [1913 Webster]