What is a word related in origin as certain words in genetically related languages descended from the same ancestral word. It is also the part of the word after all affixes have been removed.?

The Word you are looking for is "root." A root is the base form of a Word that carries its core meaning and can be traced back to a common ancestor in different languages. It is the part of a Word that remains after all affixes, prefixes, and suffixes have been removed.