Rebuff means to snub or reject someone.
- We offered to help with the cleanup, but he rebuffed us.
Rebut means to argue against something.
- Unless the board rebuts the proposal, the idea is accepted.
Refute means to prove something is false.
- The defense team refuted much of the earlier testimony.
Repudiate means to reject or refuse something.
- We were always taught to repudiate discrimination and violence.