Which prefix means 'back'?

The prefix "retro-" indeed means 'back' or 'backward.' It is commonly used in various terms to signify a return to an earlier state or condition. For example, in the word "retrospective," it indicates looking back at past events or trends. The use of "retro-" implies a sense of reversal or returning to a prior position, making it the appropriate choice for a prefix meaning 'back.'

In contrast, the prefix "sub-" typically denotes 'under' or 'below,' as seen in words like "submarine" (under the sea) or "substandard" (below standard). "Meta-" is used to signify a change or transformation, often referring to something that goes beyond or operates on a different level, as seen in "metaphysics." The prefix "macro-" refers to something large or on a grand scale, such as in "macroeconomics," which studies large-scale economic factors. Therefore, "retro-" is the most accurate prefix for conveying the meaning of 'back.'