flatfoot

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A condition in which the arch of the foot is abnormally flattened down so that the entire sole makes contact with the ground.
• noun Informal A person with flat feet.
• noun Slang A police officer.
• intransitive verb To walk in a flat-footed manner.

from The Century Dictionary.

• noun In pathology, a condition in which the arch of the foot is broken down, the sole touching the ground throughout its entire area.
• noun A condition in heavy draft-horses (usually of the fore feet), in which the heel is low, the ground-surface broad, the sole flat or slightly convex, and the wall more acutely slanted than is normal.

from the GNU version of the Collaborative International Dictionary of English.

• (Med.) 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.
• noun slang a police officer, especially a foot patrolman.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A condition in which the arch of the foot makes contact with the ground
• noun A person having the above condition
• noun colloquial, archaic, pejorative, law enforcement (plural typically flatfoots) A policeman

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a policeman who patrols a given region
• noun a foot afflicted with a fallen arch; abnormally flattened and spread out