theory

noun:a well-supported explanation of some aspect of the natural world based on evidence and testable principles
- The theory of plate tectonics explains the movement of continents.
noun:a set of principles or ideas intended to explain a particular phenomenon or set of phenomena, especially when not yet proven
- Several theories attempt to account for how languages evolve.
noun:an idea offered to explain a particular situation
- My theory is that the Wi-Fi keeps dropping because the router overheats.