Meaning

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

originFrom Portuguese sargaço (“(originally) the Lisbon false sun-rose or woolly rock rose (Halimium lasianthum); (now) gulfweed, sargasso”), ultimately from Latin salicastrum (“kind of wild vine found in willow-thickets”), from salix (“plant of the genus Salix; willow”) + -astrum (suffix forming nouns expressing incomplete resemblance). Salix is derived from Proto-Indo-European *sl̥H-ik- (“willow”).…

Etymology from Wiktionary, CC BY-SA 3.0