formative

Short definition from Wiktionary

Adjective

1. 1
   Capable of forming something.
2. 2
   Capable of forming something: Capable of producing new tissue.
3. 3
   Capable of forming something: Pertaining to the formation of words; specifically, of an affix: forming words through inflection.
4. 4
   Of or pertaining to the formation and subsequent growth of something.
5. 5
   Of a form of assessment: used to guide learning rather than to quantify educational outcomes.

Noun

1. 1
   A thing which causes formation to occur.
2. 2
   A language unit, typically a morph, that has a morphological function (that is, forming a word from a root or another word).
3. 3
   Synonym of derivative (“a word that derives from another one”).