Entry 1 sense Webster, 1913 Sargasso /sär-găs'-ō/ · Sar·gas·so · IPA /sɑɹˈɡæsoʊ/ 01 n. The gulf weed. See under Gulf. 1. The gulf weed. See under Gulf.(Bot.) See: Gulf Phrases & compounds Sargasso Sea — a large tract of the North Atlantic Ocean where sargasso in great abundance floats on the surface.