Wiktionary
friend of dorothy
n. (context slang dated euphemistic English) A homosexual man.
Wikipedia
Friend of Dorothy
In gay slang, a "friend of Dorothy" (occasionally abbreviated FOD) is a term for a gay man. The phrase dates back to at least World War II, when homosexual acts were illegal in the United States. Stating that, or asking if, someone was a "friend of Dorothy" was a euphemism used for discussing sexual orientation without others knowing its meaning. A similar term, "friend of Mrs. King" (i.e. Queen) was used in England, mostly in the first half of the 20th century.
Usage examples of "friend of dorothy".
A great friend of Dorothy and Ozma seemed to be a machine man called Tik-Tok, who ran down several times during the evening and had to be wound up again by someone before he could move or speak.