Words That Rhyme With "Neptunium" :
3 syllables:
conium, cranium, minium, rhenium
4 syllables:
ammonium, Asplenium, biennium, bucranium, calcaneum, decennium, delphinium, didinium, dominium, euphonium, geranium, germanium, harmonium, helenium, hydronium, hymenium, Iconium, illinium, ionium, Mancunian, meconium, millennium, phosphonium, polonium, proscenium, quadrennium, quinquennium, ruthenium, selenium, stramonium, sulfonium, sulphonium, syconium, triclinium, triennium, uranium, virginium, zirconium
5 syllables:
androconium, archegonium, ascogonium, bimillennium, carpogonium, chondrocranium, condominium, cuprammonium, diazonium, endocranium, Herculaneum, hydroxonium, oogonium, pandemonium, parascenium, pelargonium, pericranium, perigonium, positronium, sporogonium, succedaneum, suppedaneum, uredinium
6 syllables:
ferrozirconium, hexamethonium, spermatogonium