Entry 1 sense Webster, 1913 Oligarch /ōl'-ĭg-ärkˌ/ · Ol·i·garch · IPA /ˈɑləɡɑɹk/ 01 n. A member of an oligarchy; one of the rulers in an oligarchical government. 1. A member of an oligarchy; one of the rulers in an oligarchical government.