Quickness rhymes with:
sickness, thickness, blackness, bleakness, darkness, frankness, harkness, hawkiness, homesickness, likeness, preakness, sickness, slackness, thickness, uniqueness, weakness
Quickness sounds like:
qing, qmax, quaking, quanex, quang, quashing, queasiness, queen's, queens, queensway, quench, quenches, queuing, quickening, quickens, quina's, quince, quincey, quincy, quincy's, quinn's, quinoco, quinones, quinonez, quizzing