For example, the English words just (adj.), justify (verb), justification (noun), and justly (adverb) are all clearly a part of the same "family" although they each will have a separate dictionary entry because they are each different parts of speech.
How would I describe this "family" of words? I want to say...
The word just is a __________ of justification.
I always thought cognate was the correct word as you can tell from my ELU thread answer here: Technical term for a noun version of an adjective. But, apparently, the word applies to the case where you are comparing words from different languages. If so, what is the best term for words from the same language?