Why is the ninth month called September?
c.1400, "disciple of Aristotle," from Old French perypatetique (14c.), from Latin peripateticus "pertaining to the disciples or philosophy of Aristotle," from Greek peripatetikos "given to walking about" (especially while teaching), from peripatein "walk up and down, walk about," from peri- "around" (see peri-) + patein "to walk, tread" (see find (v.)). Aristotle's custom was to teach while strolling through the Lyceum in Athens. In English, the philosophical meaning is older than that of "person who wanders about" (1610s).
1560s in the philosophical sense, 1640s in the literal sense; see peripatetic (n.).