It’s common to use the word “notion” to refer to an idea or concept, such as “the notion of dinosaurs being ancestors of birds,” or to refer to a fanciful whim, as in, “I had a notion to call off work and take you out for lunch today.” “Notion” came into English from French, but it originated from the medieval Latin “notus,” meaning “known.” With those usages for a noun, we can extend them to an adjective, “notional,” which comes from the Latin “notionalis,” or “relating to an idea.” As an adjective, “notional” describes things that exist only as ideas, theories, or suggestions. They can be imaginary creatures with no proof of existence, or scientific concepts that still need more research to support them as fact.