Simplest rhymes with:
agriculturalist, analyst, ballast, beautifullest, calloused, capitalist, catalyst, cellist, conversationalist, coolest, cruelest, dullest, evangelist, formalist, fullest, gentlest, gollust, herbalist, humblest, institutionalist, journalist, littlest, monopolist, nationalist, naturalist, neutralist, novelist, palest, panelist, photojournalist, populist, psychoanalyst, smallest, socialist, specialist, stablest, televangelist, ultranationalist, violist