I remember knowing a term for "beginnings or endings" that are similar in many words. Not suffixes or prefixes.
I knew this term a long time ago but for some reason I can't recall it. I don't even remember examples but I'll try to make some up.
e.g. English Stackexchange, Biology Stackexchange, Chemistry stackexchange.
All these words have "stackexchange" ending. What is this "stackexchange" called? It's not suffix.
Another example: internet, internal, interjection, interest. All these words have "inter" in common. What's it called?
I apologize if there is the same existing question but finding it would be easy only if I knew the name and I don't know the name.
Thanks in advance.