principle

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A basic truth, law, or assumption.
• noun A rule or standard, especially of good behavior.
• noun The collectivity of moral or ethical standards or judgments.
• noun A fixed or predetermined policy or mode of action.
• noun A basic or essential quality or element determining intrinsic nature or characteristic behavior.
• noun A rule or law concerning the functioning of natural phenomena or mechanical processes.
• noun Chemistry One of the elements that compose a substance, especially one that gives some special quality or effect.
• noun A basic source.
• idiom (in principle) With regard to the basics.
• idiom (on principle) According to or because of principle.

from The Century Dictionary.

• To establish or fix in certain principles; impress with any tenet or belief, whether good or ill: used chiefly in the past participle.
• noun Beginning; commencement.
• noun Cause, in the widest sense; that by which anything is in any way ultimately determined or regulated.
• noun An original faculty or endowment of the mind: as, the principle of observation and comparison.
• noun A truth which is evident and general; a truth comprehending many subordinate truths; a law on which others are founded, or from which others are derived: as, the principles of morality, of equity, of government, etc. In mathematical physics a principle commonly means a very widely useful theorem.
• noun That which is professed or accepted as a law of action or a rule of conduct; one of the fundamental doctrines or tenets of a system: as, the principles of the Stoics or of the Epicureans; hence, a right rule of conduct; in general, equity; uprightness: as, a man of principle.
• noun In chem.: A component part; an element: as, the constituent principles of bodies.
• noun A substance on the presence of which certain qualities, common to a number of bodies, depend. See proximate principles, under proximate.
• noun In patent law, a law of nature, or a general property of matter, a rule of abstract science.
• noun a certain important proposition concerning the equation
• noun See the adjectives.

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb To equip with principles; to establish, or fix, in certain principles; to impress with any tenet, or rule of conduct, good or ill.
• noun obsolete Beginning; commencement.
• noun A source, or origin; that from which anything proceeds; fundamental substance or energy; primordial substance; ultimate element, or cause.
• noun An original faculty or endowment.
• noun A fundamental truth; a comprehensive law or doctrine, from which others are derived, or on which others are founded; a general truth; an elementary proposition; a maxim; an axiom; a postulate.
• noun A settled rule of action; a governing law of conduct; an opinion or belief which exercises a directing influence on the life and behavior; a rule (usually, a right rule) of conduct consistently directing one's actions.
• noun (Chem.) Any original inherent constituent which characterizes a substance, or gives it its essential properties, and which can usually be separated by analysis; -- applied especially to drugs, plant extracts, etc.
• noun etc. See under Bitter, Contradiction, etc.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A fundamental assumption.
• noun A rule used to choose among solutions to a problem.
• noun usually plural Moral rule or aspect.
• noun physics A rule or law of nature, or the basic idea on how the laws of nature are applied.
• noun A fundamental essence, particularly one producing a given quality.
• noun obsolete A beginning.
• verb transitive To equip with principles; to establish, or fix, in certain principles; to impress with any tenet or rule of conduct.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a basic truth or law or assumption
• noun a basic generalization that is accepted as true and that can be used as a basis for reasoning or conduct
• noun a rule or standard especially of good behavior
• noun (law) an explanation of the fundamental reasons (especially an explanation of the working of some device in terms of laws of nature)
• noun rule of personal conduct
• noun a rule or law concerning a natural phenomenon or the function of a complex system