Term: big-bang theory: (cosmology) the theory that the universe originated sometime between 10 billion and 20 billion years ago from the cataclysmic explosion of a small volume of matter at extremely high density and temperature
Broader: theory: a well-substantiated explanation of some aspect of the natural world; an organized system of accepted knowledge that applies in a variety of circumstances to explain a specific set of phenomena | Unrelated: plasmodiophora: type genus of Plasmodiophoraceae comprising minute plant parasitic fungi similar to and sometimes included among the slime molds
Broader: theory: a well-substantiated explanation of some aspect of the natural world; an organized system of accepted knowledge that applies in a variety of circumstances to explain a specific set of phenomena | Unrelated: galago: agile long-tailed nocturnal African lemur with dense woolly fur and large eyes and ears