A word that describes different forms of the same word

Is there a word that describes all forms of a root word (not being the past tense or past participle form)? In the instant case, the root word is "compare" and one of the different forms is "comparatively". But I want to refer to all of the different forms that "compare" could take. Please help me.

Words like 'Accidence', 'declension' or 'conjugation' may be used for derivtional words. Of the three words suggested, the first two may be used for noun derivatives and the last for verb derivatives.

The modulation of a word can well be described by the term, 'inflexion' as well.