8+ Characters of mixed case with no dictionary based word is a good start for the root password.
Brute force attacks will often use a dictionary, but can also attempt mutations of the dictionary word.
All these passwords are 8 characters; they are all very poor choices:
With less than 8 it is possible for an offline attack to try every possible combination; depending on the system speed. If you want to be sure make up something mixed with 10 characters.