Diminution rhymes with:
absolution, aleutian, andalusian, attribution, confucian, constitution, contribution, counterrevolution, devolution, dilution, dissolution, distribution, electrocution, elocution, evolution, execution, institution, lilliputian, lucian, persecution, pollution, prosecution, prostitution, redistribution, resolution, restitution, retribution, revolution, shooshan, solution, substitution
Diminution sounds like:
damnation, dandeneau, dantin, danton, dantoni, dantonio, dantuono, demotion, denden, denomination, dentin, dentine, dentino, dentition, denton, dentton, detention, detonation, diantonio, dimunition, domination, donathan, donation, downtime, downtown, dundon, dunedin, dunton