Dear Bernard, I enjoyed 'Gallows Thief' very much, and particularly the colourful and often bizarre vocabulary that your London characters used. I noticed (correct me if I'm wrong) that none of them referred to each other as 'mate', which contemporary Londoners seem to do all the time, taxi-drivers especially. Did that term of address not exist in Regency times? Sorry, this is not the most riveting of questions, but I am very much curious, and I wonder when did it ever creep into everyday use. Do you have any idea? Thank you. Paul Reid, County Cork.
The word enters the language very early - 14th Century - but its popularity seems to explode in the 19th (I'm deducing this from the citations in the OED). In Gallows Thief it's part of the 'Flash' language, which was the argot used by underworld London in the late 18th and early 19th centuries - a 'private' language so dense that some magistrate's courts employed translators. Many flash words crossed over into mainstream English, and I suspect mate was one of them . .in the jocular sense . . it already had a perfectly respectable existence as a naval rank, or to describe a wife or husband.