stapes (n.)

"stirrup-shaped bone in the middle ear," 1660s, from Modern Latin (1560s), special use of Medieval Latin stapes "stirrup," probably an alteration of Late Latin stapia, related to stare "to stand," from PIE root *sta- "to stand, make or be firm" + pedem, accusative of pes "foot" (from PIE root *ped- "foot"). This was an invented Medieval Latin word for "stirrup," for which there was no classical Latin word, as the ancients did not use stirrups.