1690s, variant of Middle English key, keye, caye "wharf" (c.1300; mid-13c. in place names), from Old North French cai (Old French chai, 12c., Modern French quai) "sand bank," from Gaulish caium (5c.), from Old Celtic *kagio- "to encompass, enclose" (cognates: Welsh cae "fence, hedge," Cornish ke "hedge"), from PIE *kagh- "to catch, seize; wickerwork, fence" (see hedge, n.). Spelling altered in English by influence of French quai.