Green’s Dictionary of Slang

(gay) an obviously, exaggeratedly homosexual man; thus adj. use; also abbr. brilli adj., effeminately sentimental.

1919		Transcript Foster Inq. in L.R. Murphy Perverts by Official Order (1989) 46: ‘The worse I could talk about myself,..the more brilliant I thought myself’.
1922-26		S. Kahn Mentality & Homosexuality 123: ‘A fairy, or fag, will many times do anything for a living if unskilled. Many brilliants depend upon the street crowds for a living’ [Simes:DLSS].
1941		G. Legman ‘Lang. of Homosexuality’ Appendix VII in Henry Sex Variants.
1947		(con. 1944) J.H. Burns Gallery (1948) 127: At closing time in her bar, some of her boys, a bit brilli, would cry on her shoulder and tell her that she was just like some elderly lady in Arkansas.
1965		Guild Dict. Homosexual Terms 5: brilliant (n., adj.): Active and successful homosexual male.
1971		A. Karlen Sexuality & Homosexuality 308: Some slang reported in the thirties died or changed meaning. Nola meant a homosexual; a brilliant or jam fag was a vain and effeminate male homosexual [Simes:DLSS].
1972		B. Rodgers Queens’ Vernacular 37: ‘Don’t bring any of your brilliant PE chums to my little bash. I couldn’t take their cute remarks about my quaint furnishings’.