Blackens rhymes with:
slackens, brackens, slackens, africans, afroamericans, akens, alaskans, american's, americans, americans', awakens, bacon's, balkans, beacons, beckons, brackens, brookens, catkins, chicken's, chickens, chickens', churkin's, deacons, dickens, dickens', dominicans, etruscans, falcons, franciscans, gascons, graningeverken's, hearkens, hichens, houchens, jamaicans, jenkens, jenkins, kokan's, lankans, lichens, likens, lincoln's, lincolns, lukens, lykens, lykins, mcjunkins, mexicans, mickens, milken's, milkens, milkens', mohicans, moroccans, mozambicans, nebraskans, new-mexicans, nickens, pelican's, pelicans, perkins, pickens, pickens', puerto_ricans, pumpkins, quickens, reckons, republican's, republicans, republicans', ricans, ripken's, slackens, slocan's, syscon's, thickens, tokens, topekans, transamerican's, vatican's, vicon's, vulcan's, vulcans, weakens, wickens, wilkens
Blackens sounds like:
balchunas, balconies, balkanize, balkans, balking, belching, belgians, belgium's, bellyaching, bilking, blackening, blackmun's, blackness, blaesing, blakeney's, blasing, blazing, bleaching, bleakness, blessing, blessings, blocking, blossoming, blossoms, blowguns, bluejeans, blushing, bolognese, bolognesi, bulging, bullishness