Which term is synonymous with 'face down' in anatomical terms?

The term synonymous with 'face down' in anatomical terminology is "prone." In anatomy, the position of a body can be described in relation to its orientation. When someone is in a prone position, they are lying flat on their stomach, with their face down. This term is widely used in various fields such as health sciences, fitness, and physical therapy to describe body positioning, especially in relation to exercises, assessments, or physical exams.

The other terms, while relevant in their own contexts, do not denote the same position. "Supine," for instance, describes a position where a person is lying on their back, thus facing upward. "Vertical" refers to an upright position, and "horizontal" implies a parallel alignment with the ground but does not specify whether the face is down or up. Therefore, "prone" clearly aligns with the definition of lying face down.