Buckthorn rhymes with:
hawthorn, airborne, bighorn, bluhdorn, buckhorn, bullhorn, cyberporn, dearborn, einhorn, elkhorn, glyndebourne, hartshorn, hawthorn, hegadorn, hirshhorn, inborn, jetborne, kilborne, layborne, longhorn, osborn, osborne, pangborn, pfefferkorn, polkinghorn, popcorn, pronghorn, sanborn, schoellhorn, seaborne, shoehorn, shopkorn, shopworn, terkhorn, unicorn, waldhorn, waterborne, whitehorn, winterbourne
Buckthorn sounds like:
backstrom, bacterium, beckstrom, bostrom, bystrom