three-deck·er /ˈθriˈdɛkɚ/
  Three-deck·er n. Naut. A vessel of war carrying guns on three decks.
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  three-decker
       n 1: made with three slices of usually toasted bread [syn: club
            sandwich, triple-decker]
       2: any ship having three decks
       3: a warship carrying guns on three decks