noun 1. an accepted or professed rule of action or conduct: a man of good principles.
2. a fundamental, primary, or general truth, on which other truths depend: the principles of government.
3. a fundamental doctrine or tenet; a distinctive ruling opinion: the principles of the Stoics.
4. (plural) right rules of conduct.
5. guiding sense of the requirements and obligations of right conduct: a man of principle.
6. fixed rule or adopted method as to action.
7. a rule or law exemplified in natural phenomena, in the construction or operation of a machine, the working of a system, or the like: the principle of capillary attraction.
8. the method of formation, operation, or procedure exhibited in a given case: a community organised on the principle of one great family.
9. a determining characteristic of something; essential quality of character.
10. an originating or actuating agency or force.
11. an actuating agency in the mind or character, as an instinct, faculty, or natural tendency.
12. Chemistry a constituent of a substance, especially one giving to it some distinctive quality or effect.
13. Obsolete beginning or commencement.
–phrase 14. in principle,
a. according to the rule generally followed.
b. as an expression of general intentions or beliefs, without consideration of real-life complications: a decision taken in principle.
15. on principle,[Middle English, from French principe (from Latin principium) + -le, noun suffix (compare syllable, etc.)]
a. according to fixed rule, method, or practice: *And just as the bushman liked, on principle, to emphasize his `independence' from his masters, while being sometimes on good terms with the individual squatter, so the digger liked it to be thought that he cared nothing for officers as a class. –russel ward, 1966.
b. according to one's personal rule for right conduct; as a matter of moral principle.
Usage: Principle is commonly confused with principal.