Define is a free firefox third party addon which allows you to search the definition of any highlighted text on google, this addon is very simple to use you just need to highlight the text and then select Define+word
After you click the option which says Define “Internet” google will show up the results which define the word internet
Install Define For Firefox
Optionally you can use this definition service from google even without this firefox addon by searching google in the following keyword format in any internet browser.
For Example – define: internet
and click google search button, you will get same results irrespective of whatever browser you are using.