hypothesis: a tentative explanation for an observation or phenomenon that can be tested by further investigation. See also null hypothesis
theory: a hypothesis (or set of hypotheses) that has been repeatedly tested or is widely accepted. It often contains some explanatory content and can be used to make predictions about natural phenomena (e.g. Darwin’s theory of evolution, Newton’s theory of gravitation, Einstein’s theory of general relativity, the microorganism theory of infectious disease)
law: a principle presented as a bold statement that explains observations and has such good predictive power that it has been accepted to be universally true (e.g. Newton’s laws of motion). A law is different from a theory because it provides information on what will happen, not why it happens. Principle and law have similar meanings in this context, although a principle may have more explanatory content