pappus vs thistledown

pappus and thistledown both are nouns.

Word	Noun	Adjective	Verb	Adverb
pappus	Yes	No	No	No
thistledown	Yes	No	No	No

As nouns, thistledown is a hyponym of pappus; that is, thistledown is a word with a more specific, narrower meaning than pappus:

pappus: calyx composed of scales or bristles or featherlike hairs in plants of the Compositae such as thistles and dandelions
thistledown: pappus of a thistle consisting of silky featherlike hairs attached to the seed-like fruit of a thistle

pappus (noun)	thistledown (noun)
calyx composed of scales or bristles or featherlike hairs in plants of the Compositae such as thistles and dandelions	pappus of a thistle consisting of silky featherlike hairs attached to the seed-like fruit of a thistle