Origin and history of talus

"anklebone," 1690s, from Latin talus "ankle, anklebone, knucklebone" (plural tali), related to or a derivative of Latin taxillus "a small die, cube" (they originally were made from the knucklebones of animals), which is of obscure origin.

"slope," 1640s, from French talus (16c.), from Old French talu "slope, mound, small hill" (12c.), probably from Gallo-Roman *talutum, from Latin talutium "a slope or outcrop of rock debris," which is perhaps of Celtic origin (compare Welsh, Breton tal "forehead, brow").

OED (1989), however, suggests derivation from root of talus (n.1) in the sense of "heel" which developed in its Romanic descendants. Mainly used of military earthwork at first; the meaning "sloping mass of rocky fragments that has fallen from a cliff" is attested by 1830.