The Collaborative International Dictionary of English v.0.48:

Flotsam \Flot"sam\, Flotson \Flot"son\, n. [F. flotter to float.
   See FFlotilla, and cf. Jetsam.] (Law)
   Goods lost by shipwreck, and floating on the sea; -- in
   distinction from jetsam or jetson. --Blackstone.
   [1913 Webster]

WordNet (r) 3.0 (2006):

flotsam
    n 1: the floating wreckage of a ship [syn: flotsam, jetsam]