Operettas rhymes with:
marietta's, mehta's, panetta's, pinetta's, vendettas, advanta's, akita's, anastas, atlanta's, augusta's, betas, cheetahs, chipetas, costas, dakota's, dakotas, data's, datas, defreitas, delta's, deltas, djakarta's, fajitas, fermenta's, freitas, gaviotas, greta's, incata's, jakarta's, kostas, kotas, lakotas, lakotas', maestas, marietta's, matas, matsushita's, mehta's, mestas, minnesota's, nafta's, panetta's, pastas, pesetas, peta's, pinetta's, placetas, preyistas, quotas, regattas, rentas, rita's, sabatista's, sabatistas, sabatistas', sandinistas, sandinistas', sense-datas, shasta's, sonatas, sowata's, stratas, suata's, sumita's, takeshita's, toyota's, toyotas, travolta's, travoltas, vendettas, vista's, vistas, zapatista's, zapatistas
Operettas sounds like:
operates, operatic, overdoes, overdose, overdoses, overheads, overheats, overrates, overrides, overtake, overtakes, overtax, overtook, overwrites