Soonest rhymes with:
cartoonist, abolitionist, accompanist, antagonist, arsonist, botanist, calvinist, cartoonist, chauvinist, cleanest, columnist, communist, conservationist, contortionist, determinist, dishonest, ernest, exhibitionist, expressionist, feminist, finest, gymnast, harnessed, honest, illusionist, impressionist, isolationist, jansenist, keenest, kienast, leanest, machinist, meanest, menaced, modernist, neoplatonist, obstructionist, organist, perfectionist, pianist, platonist, protagonist, sternest, unionist, violinist, witnessed
Soonest sounds like:
sanctity, schenectady, schuknecht, secessionist, semi-height, sense-data, sensed, singed, sinusoid, skinniest, smacked, smashed, smestad, smoggiest, smoked, smoshed, snacked, snagged, sneaked, sneezed, sonesta, succinct, sumgait, summonsed, suncoast, sunkist, sunnyside, sunset, sunstate, sunsweet, swimsuit