Where does the word “retaliate” originate and What does retaliate mean?

The word retaliate, in its Latin form, retalio, might be said to have been the equivalent of the English response, “And the same to you!” after an uncomplimentary remark.

The source was re, back, and talis, such.

Retalio thus meant “to give tit for tat, to return like for like.” In legal usage it meant “to inflict punishment similar and equal to the injury that had been sustained.”

When introduced into the English language in the seventeenth century as retaliate, a new meaning was added, “to return good for good.”

That meaning is still recorded, but in general the verb has returned to the Latin sense.