Why is the ninth month called September?
Old English fetor "chain or shackle for the feet," from Proto-Germanic *fetero (cf. Old Saxon feteros (plural), Middle Dutch veter "fetter," in modern Dutch "lace, string," Old High German fezzera, Old Norse fiöturr, Swedish fjätter), from PIE root *ped- "foot" (see foot (n.)). The generalized sense of "anything that shackles" had evolved in Old English. Related Fetters.
c.1300, from Old English gefetrian (see fetter (n.)). Related: Fettered; fettering.