Etymology is fascinating to me. Most recently I was reading about the history of the word “one”. Have you ever wondered why it’s pronounced wun instead of rhyming with own? According to the sources I’ve read (including the awesome Online Etymology Dictionary), it originally did. In fact, the word only still uses that pronunciation, and derives from the same root. The change apparently began in the 14th century in southwestern England, and by the 18th century it was in common usage.
Related: did you know that the term “one night stand” was originally used in reference to theater performance? It wasn’t until the 1960’s that it was first used in a sexual sense. Also, “one-of-a-kind” was first used in the 1960’s as well. On the other hand, “one fell swoop” was first used by Shakespeare, in Macbeth.