Ammonium rhymes with:
harmonium, pandemonium, gonium, harmonium, pandemonium, plutonium, polonium, zirconium, capernaum, condominium, cranium, didinium, geranium, gonium, hafnium, harmonium, millennium, minium, neptunium, pandemonium, plutonium, polonium, selenium, titanium, uranium, zirconium
Ammonium sounds like:
ahmann, ahn, ahonen, ahwahnee, aim, aiman, aime, aimee, aimone, aine, am, aman, amana, amann, amano, amaya, ame, ameen, amen, amey, ami, amie, amin, amino, amman, ammann, ammeen, ammo, ammon, ammonia, amnio, amo, amon, amway, amy, an, ana, anaheim, anania, anaya, ane, anemia, anemone, anew, ann, anna, annan, anne, annen, annie, anno, annoy, annum, anny, ano, anomie, anona, anway, any, anyhow, anyon, anyone, anyway, aon, aoun, aoyama, auen, auman, aumann, aune, awan, ayn, ayon