dou·ble–deck·er /ˌdʌbəlˈdɛkɚ/ noun plural dou·ble–deck·ers
something that has two levels or layers ▪ The bus we rode on was a double-decker.
— usually used before another noun ▪ We took a tour of London on a double-decker bus. ▪ double-decker trains ▪ a double-decker sandwich
— compare single-decker, triple-decker