The riddle
What Has Two Words but Thousands of Letters?
Two kinds of letters
Post office is two words, and a post office handles thousands of letters every day. The trick is that "letters" means two things. Listeners count the letters of the alphabet in a name and come up short, since post office has only ten. The riddle means mail, which a post office sorts by the sackful.
The version that starts with P
A second form of the riddle asks what starts with P, ends with E and has thousands of letters in it. The answer does not change. Post office does start with P and end with E, so the clue helps a guesser narrow the field without giving the game away.
A bit of postal history
The United States Postal Service dates its history to 1775, when the Continental Congress named Benjamin Franklin the first Postmaster General. ZIP codes arrived much later, in 1963.
Counting what the riddle counts
Post office has ten letters of the alphabet: p, o, s, t, o, f, f, i, c, e. A name on an envelope has a few more or fewer, and nobody would call the total thousands. The building handles mail by the thousand, though. Both clues are true, and the riddle never says that the two kinds of letters are the same.
Mail in another riddle
Mail turns up again in what can travel around the world while staying in a corner, where the trick lies in the word corner.