A double-decker BUS is a type of BUS that has two levels, with the upper level typically used for seating and the lower level used for luggage or standing passengers. The term 'double-decker' is often used to refer to buses with two decks, but can also refer to other types of vehicles such as trains and boats. The crossword solution for the term double-decker, e.g. is BUS, which is a three letter word.