My father told me that "beat" cops walked the "beat" with a "billy stick" (which we now call a baton). The billy stick was attached to a leather thong and it allowed the cop to twirl the stick. The cops all apparently picked up a rhythm while doing this and it was called the "beat" (as in music).
I don't know if this is true or just my dad spinning a yarn. It sounds reasonable. I think I'll check on the Internet and see if it is true.
I found this on-line. Just a little more believable than Dad's explanation.
The word "beat" has several meanings. One of these is "to make a path by repeated treading". This is still commonly used in the term "beat a path". (Definition #8 in the link below) http://dictionary.reference.com/browse/b…
No, it doesn't. "Beat" is used in other circumstances to mean a small geographic area. In some southern U.S. states, a "beat" is a subdivision of a county. A police officer's "beat" is the area he or she is responsible for patrolling, defined in terms of city blocks or the area bounded by several streets.
"Beat" as an adjective does mean "exhausted," but here "beat" in "beat cop" is a noun being used as an attributive, to designate a "cop" (police officer) who is assigned to a specific "beat."
Not all police officers are "beat cops." Detectives who don't wear uniforms are usually assigned to a squad or "detail" that investigates a certain class of crimes, such as murder, robbery or "vice." A uniformed officer could be assigned to a special "detail" too, such as guarding the mayor or police chief, or to administrative duties in a police station.