Which prefix means "below normal"?

The prefix that means "below normal" is "hypo-." This prefix is derived from Greek, where "hypo" translates to "under" or "below." In medical terminology, it is commonly used to describe a condition where something is deficient or lower than the standard or normal level. For example, "hypoglycemia" refers to a lower-than-normal level of glucose in the blood.

The other prefixes do not convey the same meaning. "Hyper-" indicates "above normal" or "excess," as seen in terms like "hypertension," which refers to high blood pressure. "Normo-" is used to denote "normal," suggesting a standard or average condition, as in "normoglycemia," which means normal blood sugar levels. The word "adequate" is not a prefix but rather a standalone term meaning sufficient or satisfactory, and does not relate to the concept of normalcy in medical terms. Thus, "hypo-" is the only prefix correctly associated with being below normal.