Where does “fatuus” come from?

fatuus (Latin) comes from Latin fātus, from Latin for, from Proto-Italic fāōr, from Proto-Indo-European bʰéh₂ti — to speak, to be talking.

fatuus (Latin): foolish, silly, simple; stupid; insipid,...

Definitions

fatuus traces back through two separate lines of ancestry.

Step	Language	Word	Meaning
1	Latin	fātus	spoken, said, told, foretold, related, predicted; having or had spoken, etc
2	Latin	for	"defective"; I speak, talk, say
3	Proto-Italic	fāōr	speak
4	Proto-Indo-European	bʰéh₂ti	to speak, to be talking

Step	Language	Word	Meaning
1	Proto-Indo-European	bʰeh₂-	to shine, glow light; to speak, say
2	Proto-Indo-European	bʰeh₂-s-ri-	—