Dullest rhymes with:
agriculturalist, analyst, ballast, beautifullest, calloused, capitalist, catalyst, cellist, conversationalist, coolest, cruelest, evangelist, formalist, fullest, gentlest, gollust, herbalist, humblest, institutionalist, journalist, littlest, monopolist, nationalist, naturalist, neutralist, novelist, palest, panelist, photojournalist, populist, psychoanalyst, simplest, smallest, socialist, specialist, stablest, televangelist, ultranationalist, violist
Dullest sounds like:
d'allest, dahlquist, dalgety, daylight, deadliest, deadlocked, delegate, delegated, delgadio, delgado, delgaudio, delicate, delight, delighted, delist, delisted, delligatti, deloused, deluged, dialect, dualist, duelist, dulcet