Definition of half deck in US English:

half deck

noun

  • A deck reaching half the length of a ship or boat, fore or aft.

    • ‘By the late act of Parliament the space Z, which is half of the half-deck, M Z, is appropriated to the seamen.’
    • ‘Atys and Rowyn were up on the half-deck, trying to steer the huge ship through the storm.’