What does endo mean?

• A. Within
• B. In
• C. On top of
• D. Cause

Answer: (A)

Endo- is a Greek prefix meaning within or inner. It’s used in medical terms to show something located inside another structure, not just on the surface. For example, endocardium is the inner lining of the heart, endoscopy is a procedure to look inside the body, and endometrium is the lining of the uterus. Because of this sense of inside or within, endo means within. The other options don’t fit because they don’t convey the idea of being located inside: “in” is a general preposition, not the specific prefix usage here; “on top of” describes exterior positioning; and “cause” is unrelated to location or inside structure.