The Collaborative International Dictionary of English v.0.48:
Siamang \Si"a*mang`\, n. [Malay si[=a]mang.] (Zool.) A gibbon (Hylobates syndactylus), native of Sumatra. It has the second and third toes partially united by a web. [1913 Webster]WordNet (r) 3.0 (2006):
siamang n 1: large black gibbon of Sumatra having the 2nd and 3rd toes partially united by a web [syn: siamang, Hylobates syndactylus, Symphalangus syndactylus]