It's good sometimes, but more often than not it can't find a definition, which doesn't make it a particularly comprehensive dictionary. And if a word is a plural or any kind of variation, it can't find it either, just the simple form of the word, and there's no way to get a definition by highlighting a word without the 's' or whatever on the end, because you have to double click, which naturally highlights the entire word.
There's just too many words it can't find.

No longer functional. If this is fixed I will be revising my review to give the extention the 5 stars it deserves when it is functional.

For those struggling to find a replacement as I was:

Definer by Lumetrium:
- seems to fulfill the same purpose in a more aesthetically pleasing package.

Hasn't been working for a while, keeps saying definition not found

No longer works, always get definition not found.

Not working for a long time.

It doesn't work anymore

Doesn't work anymore

No longer works in 2025.
Look elsewhere.

Broken, no definition found when selecting words.

Broken, while last updated 4 years ago.

NOT WORKING

Sorry

No definition found.

it's stopped working, as all the other reviews point out

NO longer works. Every word just says "Sorry No definition found"

No longer works: It's always Sorry no definition found.

Doesn't work anymore, dev hasn't said anything on github despite issue being years old, extension is dead.