triple-decker
noun
tri·ple-deck·er ˌtri-pəl-ˈde-kər 
often attributive
: something having three basic components or levels: such as
a
: trilogy
b
: a sandwich consisting of three pieces of bread and two layers of filling
c
: a 3-story dwelling with an apartment on each floor
Word History
First Known Use
1938, in the meaning defined above