WordNet (r) 3.0 (2006):

topside
    n 1: (usually plural) weather deck; the part of a ship's hull
         that is above the waterline

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "topside":
   aboard, afloat, all aboard, aloft, at the head, at the top,
   athwart the hawse, athwarthawse, before the mast, clerestory,
   in sail, on board, on board ship, on deck, on shipboard,
   on the top, on top, ridgepole, roof, roofpole, rooftop, surface,
   top, top floor, top side, topsides, upper side, upside