sidecheck

sidecheck

(ˈsaɪdˌtʃɛk)
n
(Horse Training, Riding & Manège) part of a horse's harness

side•check

(ˈsaɪdˌtʃɛk)
n.
a checkrein passing from the bit to the saddle of the harness.
[1890–95, Amer.]