Definition of "Principle" :

noun: (law) an explanation of the fundamental reasons (especially an explanation of the working of some device in terms of laws of nature)

"The principles of internal-combustion engines."

noun: a basic truth or law or assumption

"The principles of democracy."

noun: a rule or law concerning a natural phenomenon or the function of a complex system

"The principle of the conservation of mass."

noun: a basic generalization that is accepted as true and that can be used as a basis for reasoning or conduct

"Their principles of composition characterized all their works."

noun: a rule or standard especially of good behavior

"A man of principle."

noun: rule of personal conduct