Malfoy: "Good enough, I suppose. Though to have the proper meaning, you should use the legal term indemnify rather than exonerate -"

Potter: "Nice try, but no. I know exactly what that word means, Lord Malfoy."

The word is "exonerate" in Potter's prepared text, Malfoy suggests "indemnify" as if it's a legal term that means the same thing, Potter rejects this and stays with "exonerate".

There's probably something tricky Malfoy could do with "indemnify", but looking up their definitions it's not obvious to me:

exonerate:

1. (esp. of an official body) Absolve (someone) from blame for a fault or wrongdoing, esp. after due consideration of the case.

2. Release someone from (a duty or obligation).

indemnify:

1. Compensate (someone) for harm or loss: "insurance carried to indemnify the owner for loss".

2. Secure (someone) against legal responsibility for their actions.