I did a project at school once where we had to investigate the meanings and
> origins of expressions and sayings. I have just had a look in the box of
> bits in the wardrobe, and I kept this project
>
> The original was Tip for Tap, a very old expression that evolved into tit
> for tat in the mid-16th century. Tip meant a hit, a shove. Tap was a
> retaliatory hit. The meaning is a punishment meted out to pay back an
> offence, measured to be equal and proportionate. You hit me, I hit you, tit
> for tat.
i am sorry to open this old one up again, but i have come across some new information regarding the origin of the phrase "tit for tat." the origin of this phrase are still much disputed and the above is listed as one possible source, however, many believe that it was actually derived from the french phrase "tant pour tant" meaning "sop much for so much" or even the dutch phrase "dit voor dat" meaning "this for that"
the french phrase sounds a little far-off, but the dutch phrase is very similar to ours. make up your own minds fellas.
cheers.
sam