Source : Webster's Revised Unabridged Dictionary (1913)

Sargassum \Sar*gas"sum\, n. [NL.]
   A genus of alg[ae] including the gulf weed.

Source : WordNet®

sargassum
     n : brown algae with rounded bladders forming dense floating
         masses in tropical Atlantic waters as in the Sargasso Sea
         [syn: {gulfweed}, {sargasso}, {Sargassum bacciferum}]