1) Coup participant 2) One performing a coup 3) One unseating 4) One who testifies 5) Trial witness, of a sort 6) Usurper 
• (n.) One who deposes or degrades from office. • (n.) One who testifies or deposes; a deponent.
De·pos'er noun 1. One who deposes or degrades from office. 2. One who testifies or deposes; a deponent.