Source : Webster's Revised Unabridged Dictionary (1913)

Ladanum \Lad"a*num\, n. [L. ladanum, ledanum, Gr. la`danon,
   lh`danon, fr. lh^don name of a shrub, mastic; cf. Per.
   l[=a]dan, l[=a]den. Cf. {Laudanum}.]
   A gum resin gathered from certain Oriental species of
   {Cistus}. It has a pungent odor and is chiefly used in making
   plasters, and for fumigation. [Written also {labdanum}.]

Source : WordNet®

ladanum
     n : a soft blackish-brown resinous exudate from various
         rockroses used in perfumes especially as a fixative [syn:
          {labdanum}]