Sadie is a nineteenth-century American diminutive of Sarah — from the Hebrew meaning "princess." It was extremely popular in late-Victorian and Edwardian America, then faded, then returned dramatically in the 2010s.
Sadie is now in the U.S. top 100 and the U.K. top 200. The full version Sarah remains available as a more formal alternative.
Sadie does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
—
In Pythagorean numerology the letters of Sadie reduce to 2, The Peacemaker. This is a traditional interpretive system, not a factual claim about the name.