1.  instep(n = noun.body) - the arch of the foot;
is a kind of arch
is a part of foot, human foot, pes
has particulars: fallen arch, sunken arch

2.  instep(n = noun.artifact) - the part of a shoe or stocking that covers the arch of the foot;
is a kind of covering
is a part of boot, shoe, stocking

1.  The arched middle portion of the human foot next in front of the ankle joint. [1913 Webster]

2.  The part of a shoe, boot, or stocking covering the instep{1}. [PJC]

3.  That part of the hind leg of the horse and allied animals, between the hock, or ham, and the pastern joint. [1913 Webster]

instep, n.
1 the inner arch of the foot between the toes and the ankle.
2 the part of a shoe etc. fitting over or under this.
3 a thing shaped like an instep.

Etymology:
16th c.: ult. formed as IN-(2) + STEP, but immed. orig. uncert.