Why is the ninth month called September?
1520s, alteration, by similarity to fold, of blindfelled (early 14c.), past participle of blindfellan "blindfold, cover the eyes (with a bandage, etc.)," also "to strike blind" (c.1200), from Old English (ge)blindfellian "to strike blind," from blind (adj.) + Anglian gefeollan "to strike down," as in to fell a tree (see fell (v.)). Related: Blindfolded; blindfolding.
1880, from blindfold (v.).