The definitions are pulled from third-party sources. If they don't return a definition, the add-on can't show anything. I'll try to fix this in the next version.

Also, I don't mind the 1-star review, but I'm sure there's a nicer way to express your dissatisfaction. I mean, this add-on is completely free of charge and did take some time and effort to create.

It works for most words (like 99%). If it doesn't work for a few words, do you think it warrants a negative review?

Anyway, thanks for letting me know of this issue. Every review is helpful towards improving the add-on.