The Collaborative International Dictionary of English v.0.48:

mal de mer \mal de mer\ n.
   Motion sickness experienced while traveling on water;
   seasickness.

   Syn: seasickness, naupathia.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

mal de mer
    n 1: motion sickness experienced while traveling on water [syn:
         seasickness, mal de mer, naupathia]