The Collaborative International Dictionary of English v.0.48:

Irrelative \Ir*rel"a*tive\, a.
   Not relative; without mutual relations; unconnected. --
   Ir*rel"a*tive*ly, adv.
   [1913 Webster]

   Irrelative chords (Mus.), those having no common tone.

   Irrelative repetition (Biol.), the multiplication of parts
      that serve for a common purpose, but have no mutual
      dependence or connection. --Owen.
      [1913 Webster]