a very agile black gibbon (Symphalangus syndactylus) of the Malay Peninsula and Sumatra
See siamang in American Heritage Dictionary 4
(sēˈə-măngˌ, sē-ămˈəng)
noun
A large black gibbon (Symphalangus syndactylus or Hylobates syndactylus) of Sumatra and the Malay Peninsula, having an inflatable throat sac and a web of skin joining the second and third toes.