• (n.) One who impeaches.
Im·peach'er noun One who impeaches. 
impeacher 1. Someone who challenges or discredits another person's honor, reputation, etc. 2. Anyone who challenges the practices or honesty of; to accuse; especially, to bring (a public official) before a proper tribunal or legal authority on a charge of wrong-doing. Whenever anyone demands that a public official should be impeached, that person...