Noumenon and Thing-in-itself

Noumenon noun - The intellectual conception of a thing as it is in itself, not as it is known through perception.

Thing-in-itself is a synonym for noumenon. In some cases you can use "Thing-in-itself" instead a noun "Noumenon". popular alternative

Thing-in-itself noun - The intellectual conception of a thing as it is in itself, not as it is known through perception.

Noumenon is a synonym for thing-in-itself. You can use "Noumenon" instead a noun phrase "Thing-in-itself".