Which prefix means 'backward' or 'behind'?

The prefix that indicates 'backward' or 'behind' is "retro-." This prefix is commonly used in medical terminology to describe various conditions, procedures, or anatomical positions that involve a backward orientation or a return to a previous state. For example, "retrograde" refers to the movement or flow of a substance in the opposite direction, often used in contexts like blood flow or nerve impulses.

In contrast, the other prefixes convey different meanings: "trans-" relates to across or through, "semi-" means half or partly, and "sub-" indicates below or beneath. Understanding the meanings of these prefixes is crucial for interpreting medical terms accurately, allowing for a clearer understanding of health-related texts and discussions.