The word “grand” is used to mean one thousand because historically, 1,000 dollars was considered a “grand amount of money.” The term “grand” itself is believed to have originated from the Old French word “grant,” which means large or great. The first written usage of the term “grand” in the context of one thousand dollars dates back to 1915.

There are a few reasons why “grand” likely caught on and persisted as slang for 1,000: It was quicker to say than “one thousand.” Its origins from the pound-shilling system gave it an authoritative air. “Grand” also means splendid or impressive, so the word suggests the large nature of the 1,000 amount.

During WWII, the Yanks brought the term to the UK, where it came to mean £1,000. By the late 1940s, a grand meant a thousand of almost anything, not just money.