Epi-

CIDE DICTIONARY

Epi-,  [Gr. 'epi` on, upon, to; akin to Skr. api besides, and prob. to L. ob to, before, on account of, and perh. to E. of, off.].

 A prefix, meaning upon, beside, among, on the outside, above, over. It becomes ep-before a vowel, as in epoch, and eph-before a Greek aspirate, as in ephemeral.  [1913 Webster]

OXFORD DICTIONARY

Epi-, prefix (usu. ep- before a vowel or h)
1 upon (epicycle).
2 above (epicotyl).
3 in addition (epiphenomenon).

Etymology

Gk epi (prep.)