Schrödinger's cat

Wiktionary

1. n. A hypothetical cat that is depicted as being surrounded by perfectly uncertain circumstances that make an external observer absolutely unable to deem the cat either alive or dead, especially if the possibilities of survival of the cat are expected to be analysed from the point of view of quantum mechanics. Typically, these circumstances involve the cat being inside a box while being the victim of a danger that may or may not kill it, such as radiation.
2. n. by extension Any hypothetical situation whose circumstances make it impossible to see which among two contrary propositions is correct, especially if the situation is expected to be analysed from the point of view of quantum mechanics.
3. n. The thought experiment which was devised by Erwin Schrödinger, is usually considered a paradox, involves a Schrödinger's cat and is typically supposed to be analysed from the point of view of quantum mechanics.
4. n. A Schrödinger's cat (a hypothetical cat that may or may not be dead) in particular, especially when implied to be the only Schrödinger's cat in the world.