General:
* Understanding: The ability to comprehend something.
* Unity: The state of being united or joined together.
* Unanimity: Complete agreement.
* Uncertainty: Doubt or a lack of confidence.
* Usefulness: The quality of being useful or helpful.
* Upheaval: Great disorder or change.
* Utility: The state of being useful.
More Specific:
* Ubiquity: The state of being everywhere at once.
* Unconsciousness: The state of being unaware of one's surroundings.
* Utterance: Something that is spoken.
* Undertaking: A task or project.
* Unrest: A state of anxiety or disturbance.
* Uprightness: The quality of being honest and moral.
* Usurpation: The act of taking someone's power or position illegally.
Figurative:
* Unreality: The state of not being real.
* Unfathomableness: The quality of being impossible to understand.
* Unforeseen: Something that is unexpected.
* Utopia: A perfect or ideal place.
This list is not exhaustive, but it should give you a good starting point.