suppedaneum
/ˌsʌpɪˈdeɪnɪəm/noun
A support for the feet of a crucified person, projecting from the vertical shaft of the cross, especially as represented in art.
Origin
Late 17th century; earliest use found in Samuel Wesley (bap. 1662, d. 1735), Church of England clergyman and poet. From post-classical Latin suppedaneum footstool (Vetus Latina), use as noun of neuter singular of suppedaneus.