The Collaborative International Dictionary of English v.0.48:

Jetsam \Jet"sam\, Jetson \Jet"son\, n. [F. jeter to throw: cf.
   OF. getaison a throwing. Cf. Flotsam, Jettison.]
   1. (Mar. Law) Goods which sink when cast into the sea, and
      remain under water; -- distinguished from flotsam, goods
      which float, and ligan (or lagan), goods which are
      sunk attached to a buoy.
      [1913 Webster]

   2. The act of throwing objects from a ship to lighten the
      load; jettison[1]. See Jettison, 1.
      [1913 Webster]

   3. Hence: Anything thrown overboard from a ship, whether
      floating or not.
      [PJC]

   4. Hence: [fig.] Objects scattered about in a disorderly
      manner; as, he couldn't find his sneakers among the jetsam
      in his room. [Colloq.]
      [PJC]

WordNet (r) 3.0 (2006):

jetsam
    n 1: the part of a ship's equipment or cargo that is thrown
         overboard to lighten the load in a storm
    2: the floating wreckage of a ship [syn: flotsam, jetsam]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "jetsam":
   castaway, castoff, derelict, discard, dogie, flotsam,
   flotsam and jetsam, foundling, junk, lagan, orphan, refuse, reject,
   rubbish, trash, waif, waifs and strays, wastrel, wreckage