Where does “Dinosauria” come from?

Dinosauria (Latin) comes from Ancient Greek δεινός, from Ancient Greek ὄνυξ, from Proto-Indo-European h₃nogʰ- — claw, nail; nail.

Ancestry of “Dinosauria”, step by step

Step	Language	Word	Meaning
1	Ancient Greek	δεινός	terrible, horrible, fearful, astounding; danger;...
2	Ancient Greek	ὄνυξ	claw, nail, hoof, talon; Anything which resembles...
3	Proto-Indo-European	h₃nogʰ-	claw, nail; nail