What it would be called if we have words like "history", "histories", "historic", etc? I mean, for example we have words that are synonyms, homonyms, etc, but how about words that can be stemmed to a root word? What should we call such group of words?
A word family is a group of related words that are formed from the same word. There are inflected forms with inflectional affixes (-s: help-helps,-er, -est : big-bigger-biggest, -ing :run-running, -ed: help-helped, etc.) which belong to the word and derived forms with derivational affixes (-able, -er,-ment, un-, in-, -ation, -ist, -ful,-ize, etc.) which make a word family. The core word and derived forms support the same core meaning. But derivational suffixes usually change the word class and the meaning.
help,helper, helpful, group-subgroup, dark-darkness, agree-agreement, friend -friendship.
In linguistics, the many word-forms that relate to a single unit of meaning, such as history, histories, historic etc, relate to a single lexeme. A dictionary is essentially a list of lexemes.
However this is an academic word and I don't think it will be widely understood. I looked it up to answer this question.