noun

1. the ultimate source, origin, or cause of something
2. a natural or original tendency, faculty, or endowment
3. a fundamental truth, law, doctrine, or motivating force, upon which others are based moral principles
4. 1. a rule of conduct, esp. of right conduct
   2. such rules collectively
   3. adherence to them; integrity; uprightness a man of principle
5. an essential element, constituent, or quality, esp. one that produces a specific effect the active principle of a medicine
6. 1. the scientific law that explains a natural action the principle of cell division
   2. the method of a thing's operation the principle of a gasoline engine is internal combustion

Etymology: ME, altered < MFr principe < L principium: see principium