silenus
noun
si·le·nus sī-ˈlē-nəs 
plural sileni sī-ˈlē-ˌnī
often capitalized
: a minor woodland deity and companion of Dionysus in Greek mythology with a horse's ears and tail
Word History
Etymology
Latin, from Greek silēnos, from Silēnos foster father of Dionysus
First Known Use
1572, in the meaning defined above