Source : Webster's Revised Unabridged Dictionary (1913)

Derivational \Der`i*va"tion*al\, a.
   Relating to derivation. --Earle.

Source : WordNet®

derivational
     adj : characterized by inflections indicating a semantic relation
           between a word and its base; "the morphological
           relation between `sing' and `singer' and `song' is
           derivational" [ant: {inflectional}]