an animal that is similar to a monkey but has no tail or only a very short tail.——朗文当代大辞典

An animal of the monkey tribe (Simiadæ); before the introduction of ‘monkey’ (16th cent.), the generic name, and still (since 1700) sometimes so used poetically or rhetorically, or when their uncouth resemblance to men and mimicry of human action is the main idea (due to reaction of the verb ape upon the noun whence it was formed).——牛津当代大辞典  @en