Why is the ninth month called September?
Old English fællan (Mercian), fyllan (West Saxon) "make fall, cause to fall," also "strike down, demolish, kill," from Proto-Germanic *fallijanan (cf. Old Frisian falla, Old Saxon fellian, Dutch fellen, Old High German fellen, German fällen, Old Norse fella, Danish fælde), causative of *fallan (Old English feallan, see fall (v.)), showing i-mutation. Related: Felled; feller; felling.
Old English feoll; past tense of fall (v.).
"cruel," late 13c., from Old French fel "cruel, fierce, vicious," from Medieval Latin fello "villain" (see felon). Phrase at one fell swoop is from "Macbeth."
"rocky hill," c.1300, from Old Norse fiall "mountain," from Proto-Germanic *felzam- "rock" (cf. German Fels "stone, rock"), from PIE root *pel(i)s- "rock, cliff."
"skin or hide of an animal," Old English fel, from Proto-Germanic *fellom- (cf. Old Frisian fel, Old Saxon fel, Dutch vel, Old High German fel, German fell, Old Norse fiall, Gothic fill), from PIE *pello- (see film (n.)).