Green’s Dictionary of Slang

(Aus.) an effeminate male homosexual.

a.1950		note in S.J. Baker papers MLMSS 165: Box 3: Triss = homo.
1953		K. Tennant Joyful Condemned 165: Think I’m going round flapping my mouth to every silly triss that gets shoved in with me?
1966		Trimble 5000 Adult Sex Words and Phrases.
1972		B. Rodgers Queens’ Vernacular.
1999		G. Seal Lingo 115: Later in the l9th century came the term gussie and the 20th century has contributed many more, such as [...] triss, cat (perhaps a shortening of a more or less polite 19th-century term for homosexuals, catamite, though cat may also be used as Lingo for a prostitute).