Unit Layers is a very simple, small and neat browser extension that instantly provides the definition of any highlighted word. It works with all 3 most popular Windows browsers: Firefox, Google Chrome and Internet Explorer.
Though the definitions are taken from a rather unknown source and are not always accurate, this little tool is quite handy.
It represents one of the fastest and easiest ways of getting the English definition or explanation of a word while browsing the web. Just highlight that word as you browse the page where it is displayed, and its English definition will be shown in a simple, non-customizable pop-up. Unfortunately, if the definition is not accurate enough to help you, there’s nothing else you can do about it which would involve this extension, as it doesn’t support multiple dictionaries or definition sources. You can only Google search for the right definition in a separate browser page.
Anyway, Unit Layers is free and very simple to install. It won’t hinder your usual workflow in any way and it can prove to be helpful in many situations even though it currently looks like it could be improved a lot.