Answer:
The word "rebut" is a synonym for "refute"-- in other words, to challenge what someone has just said and prove their assertion was wrong. You may have seen this word as a noun, "rebuttal." An example: The two candidates, Mary Smith and John Jones, were having a debate. Smith accused Jones of being a dishonest politician. Jones said, "Let me rebut that," and he then gave reasons why he was not dishonest.