Open Terminal, and then type this command, followed by the Return key:
defaults write com.apple.dashboard mcx-disabled -boolean YES
This tells the system that you no longer wish to have Dashboard available. However, the Dashboard task is actually “owned” by the Dock, so to make your changes take effect, you need to restart the Dock. The easiest way to do that is to type this command into the Terminal (and press Return when done):
killall Dock
After the Dock restarts, hit F12 and you’ll see…nothing at all. If you run Activity Monitor, you also won’t find any Dashboard widgets in the list of tasks, even if you had several open when you ran the above command. Dashboard has been eliminated from your system, and won’t return until you tell it to do so. You can do just that by opening Terminal again, and typing this command:
defaults write com.apple.dashboard mcx-disabled -boolean NO
Once again, you’ll have to use the killall Dock command to make the changes take effect. Once you do, though, you’ll find that Dashboard is back as usual—and any widgets you had opened on the Dashboard will still be open.