Which prefix indicates "large"?

The prefix "mega-" is used to indicate something that is large or significant in size, amount, or degree. In medical terminology and other scientific contexts, "mega-" often refers to larger than normal or extraordinarily large entities. For instance, a megabyte is a large unit of digital information, and "megacolon" refers to an abnormal enlargement of the colon.

While "macro-" is another prefix that can connote largeness, "mega-" generally conveys a stronger sense of size, particularly in clinical and medical settings. Therefore, in the context of indicating "large," "mega-" serves as the most appropriate choice.