Question: I experience reoccurring incidents of `fontd` eating up all the process power. What could be the cause of this and how do I make it behave again?

Answer: 
`sudo atsutil databases -remove; atsutil server -shutdown`

From 50% cpu usage to 1%

Source: <http://icicity.com/2014/02/13/high-cpu-usage-caused-by-fontd-on-os-x>
Simply you can do `rm -f ~/Library/Preferences/com.apple.FontRegistry.user.plist` and 90 percent I sure that your problem will be resolved!