Nous

νόος / νοῦς (noos / nous) - Mind, understanding, perception, intelligence; the faculty of recognizing, comprehending, and forming intentions. Homeric νόος precedes the contracted νοῦς.

νόησις (noēsis) - Thinking, understanding, mental apprehension; the activity of νόος. Especially prominent in later philosophical vocabulary.

νοητός (noētos) - Perceived or apprehended by the mind; intelligible, thinkable. Not originally a separate metaphysical realm.