What root word defines "light" in medical terminology?

The root word that defines "light" in medical terminology is "photo." This prefix comes from the Greek word "phōs," which means light. It is frequently used in various medical and scientific terms that pertain to light or radiation, such as "phototherapy," which refers to the use of light in treatment, and "photophobia," which denotes an aversion to light. Understanding this root helps in decoding numerous medical terms linked to light phenomena or treatments that involve light.

The other options do not pertain to light. "Pneumo" relates to air or lungs, "sarco" refers to flesh or muscle, and "poly" indicates many or multiple. Therefore, "photo" is the only option that accurately conveys the meaning of light in a medical context.