Antonym of THEORY

Theory : a supposition or a system of ideas intended to explain something, especially one based on general principles independent of the thing to be explained.
Imagination : the faculty or action of forming new ideas, or images or concepts of external objects not present to the senses.
Fact : a thing that is known or proved to be true.
Chance : a possibility of something happening.
Thought : an idea or opinion produced by thinking, or occurring suddenly in the mind.

Antonym of Theory is Fact