fallen arch

A flattening of the arched shape of the foot between the heelbone and toes. Fallen arches usually result from excessive strain and weakening of the tendons and ligaments supporting the arches. The condition may develop after standing still for extended periods, or after running on hard surfaces with insufficient arch supports. Fallen arches are treated with appropriate foot supports (orthotics) and special foot exercises.

Loss of the arched shape of the foot, with a flattening of the longitudinal arch between the heel-bone and toes. Fallen arches usually result from excessive strain, which weakens the tendons and ligaments supporting the arch. Standing still for long periods and running on hard surfaces without proper arch supports can contribute to the condition. Fallen arches may be treated with appropriate orthotics or exercises. See also flat feet.

A breaking down of the longitudinal or transverse arch of the foot, resulting in flat foot or spread foot.

The noun has one meaning:

Meaning #1: an instep flattened so the entire sole rests on the ground
  Synonym: sunken arch