Naphtha rhymes with:
agatha, aletha, anantha, aretha, atha, bartha, bertha, bolitho, botha, calantha, cleantha, cliantha, diantha, eartha, hertha, hiawatha, hyacintha, iantha, inkatha, jacintha, juditha, katha, letha, martha, mccartha, mintha, murtha, philantha, ramtha, samantha, tabitha, tregurtha
Naphtha sounds like:
nabbed, nafta, naivete, napped, neft, neophyte, nevada, nevitt, nifty, niobite, nipped, nobody, nobody'd, nobuto, nonfat, nonfood, novato, numbed