You had:
Widgets (main keyword)
widget
red widget
buy widget
new widget
old widget
used widget
etc...
However, Google AdWords provides you with an easy to use tool called the Keyword Tool. Seen in the picture you have two options, Keyword Variations and Site-related Keywords. The Site-related version is cool, but is a little useless. This tool just tells you what the main keyword for your site is.
With the Keyword Variations you put in a keyword, like widgets, and returned is a list of sometimes hundreds of keywords. Then if you scroll down, you can "Add All" to your keyword list, then add those straight to your Campaign > Ad Group. Easily add hundreds of keywords!
Without tools like these, we would be scouring the web for related keywords and other ways to match keywords. Leave it up to Google and they'll make your life easier!
