Why is the ninth month called September?
"coarse grass-like plant growing in wet places," Old English secg "sedge, reed, rush," from Proto-Germanic *sagjoz (cf. Low German segge, German Segge), probably from PIE root *sek- "to cut" (see section (n.) and cf. Old English secg, identical in form but meaning "sword;" and cf. German schwertel-gras "sedge" from schwert "sword"), on notion of plant with "cutting" leaves (cf. etymological sense of gladiolus). Old Irish seisg, Welsh hesgreed "rush" might represent a similar sense development from the same root. Often spelled seg, segg until present form triumphed early 1900s.