Which prefix denotes "single" or "one"?

The prefix "mono-" is used in medical terminology as well as in many other scientific contexts to denote "single" or "one." For example, "monocyte" refers to a type of white blood cell that is single-nucleated, while "monotherapy" refers to treatment with a single drug. This prefix is derived from the Greek word "monos," which means "single" or "alone." Its specific meaning is crucial in distinguishing various medical conditions and treatments that involve singular entities.

The other prefixes, such as "multi-" and "tri-," indicate multiple or three, respectively, while "tetra-" refers to four. These prefixes serve their own specific purposes in medical terminology but do not denote the concept of "single" or "one." Therefore, "mono-" is the correct choice for indicating this idea.