* Epi means "on, upon, or outside of". It indicates something located on the surface of or external to a structure.
* Endo means "inside or within". It indicates something located within or internal to a structure.
Here are some examples to illustrate the difference:
* Epidermis: The outermost layer of skin.
* Endocardium: The inner lining of the heart.
* Epicardium: The outer layer of the heart.
* Endometrium: The inner lining of the uterus.
Therefore, epi and endo are opposites in terms of location, with epi indicating an outer position and endo indicating an inner position.