Collins English-English Dictionary

principle ['prɪnsɪp^əl]

1. 1. n a standard or rule of personal conduct

   a man of principle

2. 2. n [often plural] a set of such moral rules

   he'd stoop to anything

   he has no principles

3. 3. n adherence to such a moral code; morality

   it's not the money but the principle of the thing

   torn between principle and expediency

4. 4. n a fundamental or general truth or law

   first principles

5. 5. n the essence of something

   the male principle

6. 6. n a source or fundamental cause; origin

   principle of life

7. 7. n a rule or law concerning a natural phenomenon or the behaviour of a system

   the principle of the conservation of mass

8. 8. n an underlying or guiding theory or belief

   the hereditary principle

   socialist principles

9. 9. n [chem] a constituent of a substance that gives the substance its characteristics and behaviour

   bitter principle

10. 10. n [Etymology] C14: from Latin principium beginning, basic tenet

11. 11. n [Usage] principle and principal are often confused: the principal (not principle) reason for his departure; the plan was approved in principle (not in principal)