The story
Championed as the science of ideas by Patrick M. Gunkel (1947–2017), from ideo- + -nomy. Although Gunkel stated on the “About” page of his ideonomy website that “supposedly the word ideonomy was first coined by the French Encyclopedists” to refer to a science of ideas, no direct evidence of this coinage has been found to date.
Etymology from Wiktionary, CC BY-SA 4.0.