cudweed vs herba impia

cudweed and herba impia both are nouns.

Word	Noun	Adjective	Verb	Adverb
cudweed	Yes	No	No	No
herba impia	Yes	No	No	No

As nouns, herba impia is a hyponym of cudweed; that is, herba impia is a word with a more specific, narrower meaning than cudweed:

cudweed: any plant of the genus Filago having capitate clusters of small woolly flower heads
herba impia: (literally an undutiful herb) a variety of cotton rose

Other hyponyms of cudweed include Filago germanica.

cudweed (noun)	herba impia (noun)
any of numerous plants of the genus Gnaphalium having flowers that can be dried without loss of form or color	(literally an undutiful herb) a variety of cotton rose
any plant of the genus Filago having capitate clusters of small woolly flower heads
perennial cottony-white herb of southwestern United States