Good to meet you, greeting from nearby Indianapolis. You are right about the concept not being well understood in the States, I have the same experience. All the recommendations you have received are excellent.
I use a quite "non-catchy" definition: "The circular economy is an industrial model designed and managed around circular flows of renewable, long-lasting, high value, low carbon, low entropy, low waste, non-toxic resources, products and processes. It is the systemic solution for a sustainable advanced economy, operating within and not against natural processes and the Earth’s capacity to support life in all its diversity. It aims to have a positive impact and optimal performance on all three sustainability dimensions: society, environment and economy."
For something more catchy, you might say: Nature does not create waste, we do. Nature operates in circles, we operate in lines. Nature changes slowly, we go fast. Circular economy brings man-made systems closer to ecosystems and that's a good thing.
A picture might be the best explanation. There are plenty to choose from or it would be fun to create your own.