General concepts:
* Peace
* Pain
* Patience
* Power
* Passion
* Possibility
* Progress
* Purpose
* Pride
* Pleasure
* Poverty
* Perfection
* Presence
* Precision
* Perseverance
* Policy
* Philosophy
* Prosperity
* Probability
* Protection
More specific concepts:
* Painfulness
* Patience
* Passionateness
* Possibility
* Permissiveness
* Popularity
* Predictability
* Prejudice
* Privacy
* Privilege
* Proof
* Purity
* Perspective
* Planning
* Performance
* Perception
* Peril
* Potency
* Presence
* Pressure
* Pride
* Proof
* Prosperity
* Punishment
* Productivity
This list is not exhaustive, but it should give you a good starting point. You can also use a dictionary or thesaurus to find more abstract nouns starting with "P".