ex·pan·sion·ist I. \-ch(ə)nə̇st\noun (-s) : one who favors expansionism: a.: an advocate of an enlarged paper currency b.: an advocate of territorial expansion II. adjective : practicing, advocating, or tending toward expansion; specifically: pressing for a policy of extending a nation's political and economic dominance < we must make it perfectly clear that we are not ourselves expansionist — H.L.Stimson >