The Collaborative International Dictionary
instop
Instep \In"step\, n. [Formerly also instop, instup.]
The arched middle portion of the human foot next in front of the ankle joint.
The part of a shoe, boot, or stocking covering the instep[1].
That part of the hind leg of the horse and allied animals, between the hock, or ham, and the pastern joint.
Wiktionary
instop
vb. (context transitive English) To stop; close; shut; make fast.