gulfweed

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of several brownish seaweeds of the genus Sargassum having rounded air bladders and often forming dense, floating masses in the Atlantic Ocean.

from The Century Dictionary.

• noun A coarse olive seaweed, Sargassum bacciferum, belonging to the suborder Fucaceæ.

from the GNU version of the Collaborative International Dictionary of English.

• noun A brown seaweed (Sargassum bacciferum) with rounded bladders forming dense floating masses in tropical Atlantic waters as in the Sargasso Sea.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun sargassum

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun brown algae with rounded bladders forming dense floating masses in tropical Atlantic waters as in the Sargasso Sea