There are 567 words beginning in "epi" in Webster's Second International. In the 2of12 dictionary, which contains common words, you get these:
grep ^epi /usr/share/dict/2of12.txt
epic
epicenter
epicure
epicurean
epidemic
epidemically
epidemiologist
epidemiology
epidermal
epidermic
epidermis
epiglottis
epigram
epigrammatic
epigraph
epigraphy
epilepsy
epileptic
epilog
epilogue
epinephrine
epiphany
episcopacy
episcopal
episcopate
episode
episodic
episodically
epistle
epistolary
epitaph
epithelia
epithelial
epithelium
epithet
epitome
epitomize
Epicenter, epidural, epilation, and epinephrine are all words that start with the prefix epi-.
Epidemic, epidermis, epigramme, eoigraph, elileptic, epilogue, episode, epistle, epithet, epitome, epistolary, epicurian
The prefix for episode is "epi-".
One likely possibility would be "epi."
mid
epi/gastricEpi- (above)gastr (stomach)-ic (pertaining to)
The prefix in the word "seizure" is "seiz-".
intra-
Words that start with the prefix holy include:holystoneholydayholytide
Words with the prefix -im:immaterialimmatureimmobileimmortalimpartialimperfectimpossibleimpracticalimproperWords with the prefix -in:inaccurateinactiveincalculableincapableincapacitateinconceivableindescribableindiscriminateindivisibleineffectiveingrowninvisibleinvoluntary
Epi is the prefix to change to "dia". One has "epi"logue which changes to "dia"logue...a conversation.
Words that start with the prefix af:AfroAffairAfterAfghanAfoulAfraidAffordAforeAfootAffirm