the world > animals > mammals > group Ungulata (hoofed) > family Equidae (general equines) > equus caballus or horse > [noun] > defined by general characteristics (3)
a horse not domesticated or broken in; esp. in phrases referring to a mode of punishment or torture (cf. quots. s.v. draw, v. 8), and hence…
a horse or other animal positioned on the near side.
spec. Chiefly North American and Australian. An unmanageable horse.