Which prefix means 'under'?

The prefix that means 'under' is "sub-." In medical terminology, prefixes are used to modify the meaning of root words, providing clarity about locations, conditions, or relations. "Sub-" originates from Latin, meaning "under" or "below," and is commonly used in various terms, such as "subcutaneous," which refers to tissue located beneath the skin. This prefix effectively conveys a position that is lower or beneath another structure, integrating seamlessly into medical vocabulary to specify anatomical locations or conditions.