Thanks! Here is a screenshot:

http://i.imgur.com/fXYAZgm.png

Unfortunately, it's not recursive, unlike "Navigation popups" described in what is currently the top comment. They are prettier though!

This is a nice start, but I already see one issue with this that the "Navigation popup" doesn't have: nothing on the hovercard is clickable, and thus you can't go more than one level down a tree.

The navigation popups are great except that if you move the mouse off them then they close, so as you traverse down the tree you lose parents. And you kinda end up with the same issue as before only now you really have no idea how you got there because you don't even have the open tabs to guide.[0]

[0] http://imgur.com/RS0IEet.png

I prefer Chrome's extension called Google dictionary. Every time I highlight a word, it pulls up a definition. Anywhere on the web.

OS X and iOS users can do this in Chrome and Safari, I think the shortcut it selecting a word and pressing Command-Control-D or something :)

Select and Command-Control-D is right. You can also do a three finger tab. See https://en.wikipedia.org/wiki/Dictionary_(software)#Quick_ac...

Thank you! I've had this feature for about 10 minutes and I already find it indispensable.

Agreed! How have I lived without this...

Totally didn't know about this! Cheers for the heads up.

Thank you for this, I love it.