I was wondering where I could look up the antonyms of a word root? for example, I would like to find that out for endo- and epi-. I didn't find it on etymology.com. thanks.
Wiktionary sometimes lists these. For "endo-" it lists "out-, ex- exo-, ecto-" all of which have the opposite meaning.
It doesn't offer antonyms for "epi-" You might take a look at particular words and see if there are any antonyms for particular words, for example "epidermal" has an antonym "subdermal", and epidemic has "endemic", offering two different opposites.
But do take care. Just because "exo-" is an opposite to "endo" does not mean that the word beginning "exo-" makes sense. The word "endoscope" exists, but no word "exoscope", or "ectoscope".