ecranche
A type of shield, used in jousting, which had an indentation or notch to hold the lance.
historical, uncommon
The Ghent altarpiece by Jan van Eyck, dating to 1430, [...depicts men] who carry several different forms of ecranche. […] Ecranches, including those from the Gladiatoria group, have an indentation on the right side, the so-called bouche, which served as a means to keep the lance stable on horseback.
Where it comes from
Seemingly from French, ultimately derived from cran (“notch”), although the semantics of écrancher (“uncrease, unnotch”) and its derivatives seem backward.
Adapted from the Wiktionary entry ecranche (CC BY-SA 4.0).