Which prefix is used to describe a condition that is less than normal?

The prefix that indicates a condition that is less than normal is "hypo-." This prefix derives from Greek, where it means "under" or "below." It is commonly used in medical terminology to describe various conditions or states that are deficient or reduced. For example, "hypoglycemia" refers to lower-than-normal levels of glucose in the blood.

In contrast, "hyper-" denotes an excess or above-normal condition, such as in "hypertension," which refers to high blood pressure. The prefix "re-" typically indicates 'again' or 'back,' often used in terms related to returning to a previous state or doing something anew, such as "rehydrate." The prefix "pro-" means 'for' or 'in favor of,' and is not connected to measurement or comparison in this context. Therefore, the use of "hypo-" is precisely what conveys a sense of less than normal in medical language.