Also, most people in DC just call it National. Probably because the other airport also has a one word name (Dulles).
Which airport, "Reagan", "Dulles" or "BWI" ?
They don't say "Marshall" for BWI, though.
Im recent years, the city renamed the airport to Louis Armstrong airport, but no one in the city refers to it as that. Everyone still calls it Moisant. Not that we don't like Louis Armstrong, it's always been called Moisant and New Orleans really doesn't like change.
However, I can think of one counterexample: JFK airport in NYC. It used to be called Idlewild, named after some golf course I think, but was renamed to JFK (with the airport code JFK) back in the 60s. No one knows what "Idlewild" is any more.
A further tangent, but the more obvious airport code LOU is still in active use across town at Bowman Field, the city's original air field (definitely not an airport) and these days the oldest remaining continually operating air field in the country.