The TLS has an excellent review of two dictionaries of slang: one brand new and one reprinted from 1699. I thoroughly recommend that you surf off and read it here.
As an incidental point, the review contains the word equivoque, which is a beautiful synonym for ambiguity.
The purpose of early slang dictionaries was to reveal to the honest and literate world, the secret language of criminals. Without a work of reference it is all to easy for an honest man to find himself bamboozled, as this video amply demonstrates.