a small brown animal with a long tail, which uses its hands to climb trees and lives in hotcountries.——朗文当代大辞典

Any of numerous small- to medium-sized primates belonging to the one of the three families Callitrichidae, Cebidae, and Cercopithecidae, most kinds of which have long tails and live in trees in tropical countries. Also more generally: any higher primate, including the apes as well as the true monkeys.——牛津当代大辞典  @en