uncertain= not sure
uncommon= rare; not the usual; remarkable
unconscious= not within thought; not awake
undecided= not yet at the point of making a decision
unexpected= not what someone thought would happen; not predicted
unmistakable= clear; cannot be understood the wrong way; not able to be confused or misunderstood
unnecessary= not required
untidy= messy; not neat; not organized
unwise= not smart
unworthy= not deserving; not having any value