Summary: Prefixes are key morphemes in English vocabulary that begin words. The English prefix *epi-*, which means "over" or "upon," appears in a good number of English vocabulary words, such as [*epi*]dermis and [*epi*]taph. You can remember that the prefix *epi-* means "upon" from the noun [*epi*]demic, which is a widespread disease that comes "upon" people; you can also recall that *epi-* means "over" via the word [*epi*]dermis, which is the outer skin that lies "over" lower layers of skin.
