Here's what rhymes with slackish.
blackish brackish Words that almost rhyme with slackish
waggish haggish haggis lavish radish flattish raffish laddish parish vanish banish hashish clannish mannish faddish famish flatfish snappish kaddish caddish palish anguish catfish languish vanquish brandish blandish establish outlandish reestablish disestablish