The wooden trap is formed by driving a number of stakes, so as to form a palisade, in the shape of a half oval.
1570s, from Modern Latin ovalis "egg-shaped" (source of French oval, 1540s), literally "of or pertaining to an egg," from Latin ovum "egg" (see ovary). The classical Latin word was ovatus.
1560s, from Middle French ovalle "oval figure," from Medieval Latin ovalis (see oval (adj.)).