thecodont vs archosaur

thecodont and archosaur both are nouns.

Word	Noun	Adjective	Verb	Adverb
thecodont	Yes	No	No	No
archosaur	Yes	No	No	No

As nouns, archosaur is a hypernym of thecodont; that is, archosaur is a word with a broader meaning than thecodont:

thecodont: presumably in the common ancestral line to dinosaurs and crocodiles and birds
archosaur: extinct reptiles including: dinosaurs, plesiosaurs, pterosaurs, ichthyosaurs, thecodonts

Other hypernyms of thecodont include archosaurian, archosaurian reptile.

thecodont (noun)	archosaur (noun)
presumably in the common ancestral line to dinosaurs and crocodiles and birds	extinct reptiles including: dinosaurs, plesiosaurs, pterosaurs, ichthyosaurs, thecodonts