Symposiums rhymes with:
gymnasiums, abiam's, aquariums, atriums, auditoriums, axioms, caladiums, condominiums, consortium's, geraniums, gymnasiums, herbariums, honorariums, idioms, mediums, millenniums, moratoriums, pentiums, petroleum's, podiums, premiums, stadium's, stadiums, wiliams, zirconiums
Symposiums sounds like:
significance, simpkins, simpson's, simpsons, simpsons'