Sissy is an English childhood diminutive of "sister" — also the Bavarian-Austrian nickname for Empress Elisabeth of Austria-Hungary (1837-1898), known as "Sisi" or "Sissi," wife of Emperor Franz Joseph I; her tragic life and assassination by an Italian anarchist in Geneva at age 60 made her the most-mythologized empress in modern European history. *The 1955 Austrian Sissi film trilogy starring Romy Schneider was the most-watched German-language film series of its era. Sissy Spacek (born Mary Elizabeth Spacek, 1949) — American actress; Academy Award for Best Actress for Coal Miner's Daughter (1980), playing Loretta Lynn (whom she actually resembles and who personally chose Spacek for the role). Six Oscar nominations; Carrie (1976), Three Women (1977), In the Bedroom (2001). Sissy Goodwin — pioneering trans-rights educator. Sissi (musical)* — Austrian production.
Subject of countless Austrian-Hungarian Empire histories.
Sissy 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 Sissy reduce to 1, The Leader. This is a traditional interpretive system, not a factual claim about the name.