Columbus' rhymes with:
columbus, columbus, columbus, columbus, columbus, nimbus, airbus, albus, barnabas, bierbusse, bulbous, cannabis, columbus, debose, faubus, globus, harquebus, ibis, jacobus, kobus, nimbus, omnibus, paribas, phebus, phoebus, pluribus, rebus, sorbus, syllabus, turbas, vobis
Columbus' sounds like:
clamps, cleanups, climbs, clumps, colombia's, colombo's, columbia's, columbus, columbus's