Longman Dictionary of Contemporary English - principle

~ n 1 »MORAL RULE« a) a moral rule or set of ideas which makes you behave in a particular way  (She resigned on a matter of principle. | the principle of the thing spoken)  (You shouldn't just take the car without asking, it's the principle of the thing. | on principle (=because of a moral rule you follow))  (I don't eat meat on principle. | on the principle that)  (We charge no fees on the principle that education should be available for all.) b) strong ideas about what is morally right or wrong, that you try to follow in everything you do  (He has no principles; he'll do anything, as long as it's profitable. | against sb's principles (=morally wrong to that person)) 2 »RULES OF A PROCESS« a) a rule which explains the way something such as a machine works, or which explains a natural force in the universe  (the principle of the internal combustion engine | Archimedes' principle) b) principles plural the general rules on which a skill, science etc is based  (Einstein's theories form the basic principles of modern physics. | first principles (=the most important and basic rules)) 3 »BELIEF« a belief that is accepted as a reason for an action, way of thinking etc  (the principle of free markets) 4 man/woman of principle someone who has strong ideas about what is morally right or wrong 5 in principle a) if something is possible in principle, there is no good reason why it should not happen, but it has not actually happened yet  (In principle you are entitled to a financial grant, but they're difficult to claim.) b) if you agree in principle, you agree about a general plan or idea without the details  (The scheme seems O.K. in principle, but I'd like to know more details.)