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]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

FLOTSAM, or FLOTSAN. A name for the goods which float upon the sea when a
ship is sunk, in distinction from Jetsam, (q.v.) and Legan. (q.v.) Bract.
lib. 2, c. 5; 5 Co. 106; Com. Dig. Wreck, A Bac. Ab. Court of Admiralty, B.