Any scientific principle that expresses various reciprocal relationships for the behaviour of a physical system.

(physics) The observation that the sums and differences of the frequencies of spectral lines often equal other observed frequencies; a consequence of quantum mechanics.

The axiom that "machines should work; people should think".

Any of the six recommendations that arose from an investigation of decommissioning of weapons in Northern Ireland in 1996, urging all parties involved in the conflict to renounce violence and agree to disarmament before entering into all-party negotiations.

(archaic) first principles; elementary material

(management) The theory that people in an organization tend to rise (be promoted) to the level of their incompetence.

(physics) A principle in quantum mechanics that states that no two identical fermions may occupy the same quantum state simultaneously.

Based on, having, or manifesting principles / strongly adhering to, or heedful of, guiding beliefs or moral rules

simple past tense and past participle of principle

Any of several similar explanations for the nature of the universe, and for the values of its fundamental constants, that states either that the universe is as it is because otherwise we wouldn't be here to observe it, or that the very presence of intelligent life constrains the universe to be as it is.