The Collaborative International Dictionary of English v.0.48:

Medicinal \Me*dic"i*nal\, a. [L. medicinalis: cf. F.
   m['e]dicinal. See Medicine.]
   1. Having curative or palliative properties; used for the
      cure or alleviation of bodily disorders; as, medicinal
      tinctures, plants, or springs.
      [1913 Webster]

            Drop tears as fast as the Arabian trees
            Their medicinal gum.                  --Shak.
      [1913 Webster]

   2. Of or pertaining to medicine; medical.
      [1913 Webster]

WordNet (r) 3.0 (2006):

medicinal
    adj 1: having the properties of medicine; "medicative drugs";
           "medicinal herbs"; "medicinal properties" [syn:
           medicative, medicinal]

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "medicinal":
   adjuvant, alexipharmic, alterative, analeptic, corrective,
   curative, healing, iatric, medical, medicative, pharmaceutical,
   remedial, restorative, roborant, sanative, sanatory, therapeutic,
   theriac