sargasso vs sargassum

sargasso and sargassum both are nouns.

Word	Noun	Adjective	Verb	Adverb
sargasso	Yes	No	No	No
sargassum	Yes	No	No	No

As nouns, sargasso and sargassum are synonyms defined as:

sargasso and sargassum: brown algae with rounded bladders forming dense floating masses in tropical Atlantic waters as in the Sargasso Sea

Other synonyms of sargasso include gulfweed, Sargassum bacciferum.

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