What does the prefix endo- mean, and which term uses it?

• A. Within/inside; endocarditis
• B. Outside; epidermitis
• C. Between; endotheliitis
• D. Across; endomysitis

Answer: (A)

endo- means within or inside. This prefix signals that the structure being referred to lies in the interior of something else. Endocarditis clearly demonstrates this: the endocardium is the inner lining of the heart, so endocarditis is inflammation inside the heart’s inner lining. The word breaks down as endo- (within) + cardio- (heart) + -itis (inflammation), showing exactly how the prefix conveys the location. For comparison,epi- means on or upon (as in epidermis, the outer skin layer), inter- means between, and trans- means across, illustrating different spatial relationships.