Definition of 'tween decks in English:

'tween decks

plural noun

  • The space between the decks of a ship, especially that between the continuous inside decks below the main or upper deck.

    • ‘She was the reverse of comfortable in her 'tween decks, being encumbered with luggage to such a degree, that in bad weather, when most persons were below, it was difficult to pass from one end of the ship to the other.’