Formal/Logical:
* Redundancy: Emphasizes the repetition of the same idea.
* Pleonasm: Focuses on the unnecessary use of words.
* Repetition: A more general term for saying the same thing again.
* Circularity: Highlights the circular reasoning involved.
* Truism: Refers to a statement that is obviously true.
Informal/Everyday:
* Saying the same thing twice: A simple, straightforward description.
* Repeating yourself: Similar to the above, emphasizing the act of repetition.
* Going in circles: Suggests a lack of progress due to repeated arguments.
* Beating a dead horse: Implies that the point has already been made.
* Stating the obvious: Highlights the lack of new information.
The best synonym depends on the context and the specific meaning you want to convey.