The Collaborative International Dictionary of English v.0.48:

bathyscaph \bath"y*scaph\, bathyscaphe \bath"y*scaphe\n.
   navigable deep diving vessel for underwater exploration.

   Syn: bathyscape.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

bathyscaphe
    n 1: navigable deep diving vessel for underwater exploration
         [syn: bathyscaphe, bathyscaph, bathyscape]