A catarrhine monkey primarily refers to Old World monkeys belonging to the family Catarrhini. These primates are characterized by their narrow nasal septum and downward-facing nostrils. However, there are several synonyms for the term "catarrhine monkey" that are commonly used. One such synonym is "go monkeys," which stems from their scientific classification as members of the infraorder Platyrrhini. Another synonym is "apes," as catarrhines are closely related to apes, sharing many anatomical and evolutionary traits. Furthermore, the term "hominoids" can also be used interchangeably, as it refers to the superfamily that includes both apes and Old World monkeys.