It's easy enough to give thumbs to alternative common names (and add alternative common names if they are not already in the database). Then, when someone searches for "Kaffir Lily", they'll still find it. But, it the potentially offensive word won't be prominently displayed. It looks like most of the Clivia entries in the database already have at least one other common name listed and it can certainly be added to the others. Citrus hystrix has at least three common names.
That's how I dealt with this issue in the Tradescantia database where Tradescantia fluminensis and its many cultivars are often referred to under a common name that could be considered offensive.
