Source : Webster's Revised Unabridged Dictionary (1913)

Silenus \Si*le"nus\, n. [L. Silenus the tutor and attendant of
   Bacchus.] (Zo["o]l.)
   See {Wanderoo}.

Source : WordNet®

silenus
     n 1: any of the minor woodland deities who were companions of
          Dionysus (similar to the satyrs)
     2: the chief satyr in the service of Bacchus; father of
        Dionysus; usually depicted as drunk and jolly and riding a
        donkey