|a gadget; dingus; thingumbob.|
|an extraordinary or unusual thing, person, or event; an exceptional example or instance.|
|equivalence principle (ĭ-kwĭv'ə-ləns) Pronunciation Key
A principle central to General Relativity stating that a gravitational field is locally indistinguishable from the effects of inertial forces. For example, according to the equivalence principle, it is impossible for someone in a box who experiences a force pushing him to the bottom of the box to know, from the force alone, whether that force is the result of a gravitational field (the box is standing on the surface of a planet) or an acceleration (the box is being pushed by a rocket).