The Collaborative International Dictionary of English v.0.48:

Ligan \Li"gan\ (l[imac]"gan), n. [Cf. L. ligare to bind, to tie,
   ligamen band, bandage, E. ligament, or ligsam.] (Law)
   Goods sunk in the sea, with a buoy attached in order that
   they may be found again. See Jetsam and Flotsam. [Written
   also lagan.] --Blackstone.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ligan
    n 1: goods (or wreckage) on the sea bed that is attached to a
         buoy so that it can be recovered [syn: lagan, lagend,
         ligan]