prin·ci·ple
[prin-suh-puh l]
–noun
1.an accepted or professed rule of action or conduct: a person of good moral principles.2.a fundamental, primary, or general law or truth from which others are derived: the principles of modern physics.
3.a fundamental doctrine or tenet; a distinctive ruling opinion: the principles of the Stoics.
4.principles, a personal or specific basis of conduct or management: to adhere to one’s principles; a kindergarten run on modern principles.
5.guiding sense of the requirements and obligations of right conduct: a person of principle.
6.an adopted rule or method for application in action: a working principle for general use.
7.a rule or law exemplified in natural phenomena, 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 organized on the patriarchal principle.
9.a determining characteristic of something; essential quality.
10.an originating or actuating agency or force: growth is the principle of life.
11.an actuating agency in the mind or character, as an instinct, faculty, or natural tendency: the principles of human behavior.
12.Chemistry . a constituent of a substance, especially one giving to it some distinctive quality or effect.
13.Obsolete . beginning or commencement.
—Idioms
14.in principle, in essence or substance; fundamentally: to accept a plan in principle.
15.on principle,
a.according to personal rules for right conduct; as a matter of moral principle: He refused on principle to agree to the terms of the treaty.
b.according to a fixed rule, method, or practice: He drank hot milk every night on principle.