General:
* Hypothesis: A proposed explanation made on the basis of limited evidence as a starting point for further investigation.
* Concept: A general idea or understanding.
* Model: A representation of something, often used for explanation or prediction.
* Framework: A set of principles, rules, and ideas that provides a structure for understanding something.
* Principle: A fundamental truth or belief that serves as the basis for reasoning or action.
* Idea: A thought or suggestion.
* Proposition: A statement or assertion that is put forward for consideration.
Specific to science:
* Law: A statement that describes a universal relationship between phenomena.
* Principle: A fundamental truth or rule that governs a particular area of science.
Specific to social sciences:
* Perspective: A particular point of view or way of looking at something.
* School of thought: A group of people who share similar ideas and approaches.
* Paradigm: A set of beliefs and assumptions that guide scientific research and practice.
Specific to arts and humanities:
* Approach: A way of dealing with or thinking about something.
* Method: A systematic way of doing something.
Ultimately, the best word to use will depend on the specific meaning of "theory" in the context you are using it.