The Collaborative International Dictionary of English v.0.48:

Derivational \Der`i*va"tion*al\, a.
   Relating to derivation. --Earle.
   [1913 Webster]

WordNet (r) 3.0 (2006):

derivational
    adj 1: 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]