A Cnoön is an inhabitant of the Hylaean Theoric World. Common generalizations include geometric shapes such as isosceles triangles. Cnoöns do not include natural constants such as the speed of light that vary from universe to universe and result in the differences between the Geometers and Arbreans.
Given the introduction's definition for the use of dieresis ("gets a syllable all its own"), "cnoön" may be pronounced like "know-on", which would make it an awesomely terrible pun name for a discrete particle of knowledge.
In Arabic, a law of science or mathematics is referred to as a "ka-noon", which "cnoön" may be referencing.
Cnoöns seem identical to Plato's Theory of Forms.