principle

[prin-suh-puh l] /ˈprɪn sə pəl/
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,
  1. 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.
  2. according to a fixed rule, method, or practice:
    He drank hot milk every night on principle.
Origin
1350-1400; Middle English, alteration of Middle French principe or Latin prīncipium, on the analogy of manciple. See principium
Can be confused
principal, principle (see usage note at principal; see synonym study at the current entry)
Synonyms
1, 2, 3. Principle, canon, rule imply something established as a standard or test, for measuring, regulating, or guiding conduct or practice. A principle is a general and fundamental truth that may be used in deciding conduct or choice: to adhere to principle. Canon, originally referring to an edict of the Church (a meaning that it still retains), is used of any principle, law, or critical standard that is officially approved, particularly in aesthetics and scholarship: canons of literary criticism. A rule, usually something adopted or enacted, is often the specific application of a principle: the golden rule. 2. theorem, axiom, postulate, proposition. 5. integrity, probity, rectitude, honor.
Usage note
See principal.
British Dictionary definitions for on principle

principle

/ˈprɪnsɪpəl/
noun
1.
a standard or rule of personal conduct: a man of principle
2.
(often pl) a set of such moral rules: he'd stoop to anything, he has no principles
3.
adherence to such a moral code; morality: it's not the money but the principle of the thing, torn between principle and expediency
4.
a fundamental or general truth or law: first principles
5.
the essence of something: the male principle
6.
a source or fundamental cause; origin: principle of life
7.
a rule or law concerning a natural phenomenon or the behaviour of a system: the principle of the conservation of mass
8.
an underlying or guiding theory or belief: the hereditary principle, socialist principles
9.
(chem) a constituent of a substance that gives the substance its characteristics and behaviour: bitter principle
10.
in principle, in theory or essence
11.
on principle, because of or in demonstration of a principle
Usage note
Principle and principal are often confused: the principal (not principle) reason for his departure; the plan was approved in principle (not in principal)
Word Origin
C14: from Latin principium beginning, basic tenet

Principle

/ˈprɪnsɪpəl/
noun
1.
(Christian Science) another word for God
Word Origin and History for on principle

principle

n.

late 14c., "origin, source, beginning; rule of conduct; axiom, basic assumption; elemental aspect of a craft or discipline," from Anglo-French principle, Old French principe "origin, cause, principle," from Latin principium (plural principia) "a beginning, commencement, origin, first part," in plural "foundation, elements," from princeps (see prince). Used absolutely for (good or moral) principle from 1650s.

It is often easier to fight for principles than to live up to them. [Adlai Stevenson, speech, New York City, Aug. 27, 1952]
Scientific sense of "general law of nature" is recorded from 1802. The English -l- apparently is by analogy of participle, etc.

on principle in Medicine

principle prin·ci·ple (prĭn'sə-pəl)
n.

  1. A basic truth, law, or assumption.

  2. A rule or law concerning the functioning of natural phenomena or mechanical processes.

  3. One of the elements composing a chemical compound, especially one that gives some special quality or effect.

  4. The essential ingredient in a drug.

Idioms and Phrases with on principle

on principle

.
On moral or ethical grounds. As James Russell Lowell wrote about Alexander Pope in 1871, “There was a time when I could not read Pope, but disliked him on principle.” [ First half of 1800s ]
.
According to a fixed rule or practice. For example, The police were locking up the demonstrators on principle. [ First half of 1800s ]
.
on general principle. For no special reason, in general, as in Dean won't touch broccoli on general principle. [ First half of 1800s ]

principle

see: