Kuiper is a proper noun that refers to a famous Dutch-American astronomer. However, if you are looking for synonyms for the word "kuiper" in the general sense, you could use terms such as "astrophysicist," "cosmologist," or "space scientist". Alternatively, you could refer to the object in space named after Gerard Kuiper himself: the "Kuiper Belt." This is a disc-shaped region beyond Neptune that is populated by icy bodies and comets, often referred to as "trans-Neptunian objects" or "Kuiper Belt Objects." Other possible synonyms for "kuiper" could include "planetologist," "astronomy expert," or "celestial researcher.