The Collaborative International Dictionary of English v.0.48:

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.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rockrose \Rock"rose`\, n. (Bot.)
   A name given to any species of the genus Helianthemum, low
   shrubs or herbs with yellow flowers, especially the European
   Helianthemum vulgare and the American frostweed,
   Helianthemum Canadense.
   [1913 Webster]

   Cretan rockrose, a related shrub (Cistus Creticus), one
      of the plants yielding the fragrant gum called ladanum.
      [1913 Webster]

WordNet (r) 3.0 (2006):

ladanum
    n 1: a soft blackish-brown resinous exudate from various
         rockroses used in perfumes especially as a fixative [syn:
         labdanum, ladanum]