Riposte

This is technically a fencing move. From Wikipedia:

[…] with the intent of hitting one’s opponent made by the fencer who has just parried an attack.

So, the idea is that your opponent attacks, you parry, then immediately fire back with a riposte.

However, I have tended to hear this word in the context of verbal debate, which leads to an alternative usage:

To retort quickly

So, a “comeback,” basically. Someone says something to you, and you verbally demolish them with some amazing response.

It’s from the Italian riposta, meaning to reply or response.