Fthenakis rhymes with:
dukakis, dukakis', kochis, mitsotakis, papadakis, psarouthakis, bacchus, bacus, bartkus, bilirakis, butkus, dacus, demarcus, dukakis, dukakis', firkus, funchess, hodgkiss, hotchkiss, karydakis, kochis, mitsotakis, moncus, norkus, papadakis, petkus, petrakis, psarouthakis, sarkis, vlahakis, wilkis, wirkus
Fthenakis sounds like:
fading, fadness, fathoms, fattening, feeding, feedings, fetting, feuding, fidenas, fiefdoms, fifteens, fitness, fitting, fittings, footing, footings, futons