Simultaneous rhymes with:
percutaneous, spontaneous, contemporaneous, extraneous, miscellaneous, percutaneous, spontaneous, acrimonious, aeneas, aerolineas, antonius, bournias, contemporaneous, cyrenius, erroneous, extraneous, felonious, fresenius, harmonious, homogeneous, igneous, ignominious, instantaneous, miscellaneous, morphonios, palonius, parsimonious, percutaneous, phineas, plinius, sanctimonious, spontaneous, thelonius, unceremonious, vilnius
Simultaneous sounds like:
simulating, simulations, smelting