Which prefix denotes being "below or beneath"?

The prefix "hypo-" is derived from Greek, meaning "under," "beneath," or "below." It is often used in medical terminology to indicate that something is at a lower level or concentration than normal. For instance, the term "hypoglycemia" refers to a condition where blood sugar levels are lower than acceptable or normal ranges.

In contrast, the other prefixes have different meanings: "macro-" typically refers to something that is large or enlarged, "retro-" means backward or behind, and "tri-" signifies three. Each of these prefixes serves specific contexts in communication but do not convey the idea of being below or beneath. Therefore, "hypo-" is the appropriate choice for the question.