What does "Tachy-" primarily indicate?

The prefix "Tachy-" comes from the Greek word "takhus," meaning "fast" or "swift." In various medical and scientific contexts, it is used to denote speed or rapidity. For instance, in terms like "tachycardia," which refers to a rapid heart rate, "tachy-" accurately conveys the concept of increased speed. This prefix is fundamental in differentiating conditions or phenomena that occur at an accelerated pace compared to their normal or expected rates.

While terms like "above," "beyond," and "excess" may relate to other prefixes, they do not align with the specific meaning of "Tachy-." Therefore, "C. Fast" is the most accurate interpretation of this prefix in its common usage.