Meaning of “boroughs of New York City”

Question

What does borough mean?
Does the word have a different meaning when used in the five boroughs of New York City?

Answer 1

In the US, a "borough" is a unit of government within a state. It's kind of like a town, but in the US, a town has a specific form of government that differs a bit from that of a borough, although the exact meaning differs from state to state.

In reference to New York City, a borough refers to a semi-autonomous government unit within the city. Prior to 1898, "New York City" basically referred only to what is now called Manhattan. Brooklyn was a separate city, Queens was a county composed of smaller villages, etc. These areas joined together to form what we now know as New York City in 1898. Each borough is basically a county unto itself.

Answer 2

To me as a Londoner, a borough simply refers to a district with the larger city that has some degree of administrative independence. I believe the usage is fairly similar elsewhere, in New York for example.

Wiktionary gives the following definitions for borough:

1. (obsolete) A fortified town; a town or city.
2. A town having a municipal corporation and certain traditional rights.
3. An administrative district in some cities, e.g., London.
4. An administrative unit of a city which, under most circumstances according to state or national law, would be considered a larger or more powerful entity; most commonly used in American English to define the five counties that make up New York City.
5. Other similar administrative units in cities and states in various parts of the world.
6. A district in Alaska having powers similar to a county

The first definition, although not really in use any more, is perhaps the most interesting, in that it reflects the original meaning of the word in all Germanic languages - a fortified town/city. The word "borough" indeed derives from the Old English "burh", and is state to be "Cognate with Dutch burg, German Burg, Swedish borg, Persian bur."