Diminishing rhymes with:
finishing, photofinishing, refinishing, admonishing, astonishing, banishing, finishing, furnishing, photofinishing, punishing, refinishing, replenishing, tarnishing, vanishing
Diminishing sounds like:
damaging, dancing, dehumanizing, demagoguing, demjanjuk, demjanjuk's, demonizing, denison's, denizens, denkins, denouncing, dimensions, dinkins, dinkins', dominicans, doomsaying, downsizing, downsizings, downswing, duensing, dungeons