Is there a dictionary of 19th-century gay slang ?
i do not know of any work specifically focusing on gay slang but there are several webpages and a few books documenting what can still be retrieved of the history of ‘polari’ a gay language spoken (mainly in london) from the end of the eighteenth century until the 1950s. i have given a couple of links to get you started. the story that ‘earnest’ meant ‘homosexual’ is not generally accepted by most scholars. the suggestion does not seem to appear before its being suggested by theo aronson (a long time after wilde’s own era) and sir donald sinden did substantial private research which seems to disprove the connection. (the ‘earnest’ story is too long and interesting to go into here – but again the wikipedia link will give you a flying start).