Tertius rhymes with:
pontius, porteous, agius, ambrosius, beckius, blasius, brixius, brosius, cornelious, crecelius, dinius, flavius, graffius, gurganious, iglesias, junius, lanius, launius, lenius, melius, milius, moebius, nevius, pastorius, pocius, pontius, porteous, redenius, sartorius, silvius, tullius
Tertius sounds like:
tarots, tarts, tetrads, third's, thirds, thirties, thirty's, thordis, thortec, threads, threats, throats, thwarts, tirades, tortoise, tortoises, torts, tortuous, tourette's, touretzky, towards, trade's, trades, traits, treads, treaties, treatise, treatises, treats, treaty's, triad's, triads, tridex, tritch, trites, tritsch, tritz, trots, trotsky, trout's, trudge, trudges, truths, tryouts, turrets, twardowski, twothirds