A rough equivalent in English would be “something that is thought”, or “the object of an act of thought”.
The noumenon (/ˈnɒuːmᵻnɒn/, from Greek: [εν]νοούμενον) is a posited object or event that exists without sense or perception. The term noumenon is generally used in contrast with or in relation to phenomenon, which refers to anything that can be apprehended by or is an object of the senses. Modern philosophy has generally been skeptical of the possibility of knowledge independent of the senses, and Immanuel Kant gave this point of view its canonical expression: that the noumenal world may exist, but it is completely unknowable through human sensation. In Kantian philosophy, the unknowable noumenon is often linked to the unknowable “thing-in-itself” (in Kant’s German, Ding an sich), although how to characterize the nature of the relationship is a question yet open to some controversy.
And, for this, no tears are enough to wash Your noumenal feet.
– Ramesh Balsekar