D defs.my
Entry 1 sense Webster, 1913

flat foot

/flăt fo͝ot/ · flat· foot · IPA
01 A foot in which the arch of the instep is flattened so that the entire sole of the foot rests upon the ground; also, the deformity, usually…
  1. 1.
    A foot in which the arch of the instep is flattened so that the entire sole of the foot rests upon the ground; also, the deformity, usually congential, exhibited by such a foot; splayfoot.(Med.)