below decks Syllabification: (be·low decks) (also below deck)Definition of below decks adjective & adverb in or into the space below the main deck of a ship: [as adjective]:the sleeping quarters were below decks [as adverb]:nuclear weapons stored below decks noun (belowdecks) the space below the main deck of a ship. below decks in other Oxford dictionaries Definition of below decks in the British & World English dictionary