"Titfer, Tit for tat - Hat!" - yes hrodelbert - but the question was, what is the source of Tit for Tat, not what is it rhyming slang for.

In my last post I accidentally referred to "back slang" when I meant "rhyming slang". Back slang is a totally different system. In Victorian London, for example "cool - the namesclop" would be "look - the policeman". I suspect that the later expression "Cool it!" might have owed something to that.

Anybody give any other examples of back slang or rhyming slang which have passed into the language to such an extent that people using them don't realise they are rhyming or back slang at all?