Where does “formidable” come from?

formidable (Middle French) comes from Latin formidabilis, from Latin formido, from Proto-Indo-European dʰer- — to support; to hold.

Ancestry of “formidable”, step by step

Step	Language	Word	Meaning
1	Latin	formidabilis	Causing or inspiring fear, terrible, frightening,...
2	Latin	formido	I dread or fear; I am afraid of or for; fear,...
3	Proto-Indo-European	dʰer-	to support; to hold

formidable — Etymology, Origin & Word History | Etymology Explorer