flat·foot 
(flătft′)
(flătft′)n.
1. pl. flat·feet (-fēt′) A condition in which the arch of the foot is abnormally flattened down so that the entire sole makes contact with the ground.
2. pl. flat·foots
a. Informal A person with flat feet.
b. Slang A police officer.
intr.v. flat·foot·ed, flat·foot·ing, flat·foots
To walk in a flat-footed manner: "He flatfooted along, twirling his club" (James T. Farrell).