Plutonium rhymes with:
ammonium, gonium, harmonium, pandemonium, polonium, zirconium, ammonium, capernaum, condominium, cranium, didinium, geranium, gonium, hafnium, harmonium, millennium, minium, neptunium, pandemonium, polonium, selenium, titanium, uranium, zirconium
Plutonium sounds like:
paladin, paladino, palatine, paldon, palladino, palladium, pallidotomy, palton, pelton, piltdown, platen, platinum, platona, platoon, platten, plowden, plutonian, politano, pollution, poppleton, population, poulton