water flaxseed vs duckweed

water flaxseed and duckweed both are nouns.

Word	Noun	Adjective	Verb	Adverb
water flaxseed	Yes	No	No	No
duckweed	Yes	No	No	No

As nouns, duckweed is a hypernym of water flaxseed; that is, duckweed is a word with a broader meaning than water flaxseed:

water flaxseed: cosmopolitan except South America and New Zealand and some oceanic islands
duckweed: any small or minute aquatic plant of the family Lemnaceae that float on or near the surface of shallow ponds

water flaxseed (noun)	duckweed (noun)
cosmopolitan except South America and New Zealand and some oceanic islands	any small or minute aquatic plant of the family Lemnaceae that float on or near the surface of shallow ponds