This article describes an approach in which students develop and apply definitions prior to their formal introduction to new vocabulary. The example given is an inquiry-based lesson on geologic principles. This approach is illustrated with a lesson that has been used with high school Earth science students on the principles of stratigraphy, though the lesson can be modified for other science classes as well. The article details a 60-minute lesson in 5E format--Engage, Explore, Explain, Elaborate, and Evaluate. A stratigraphic layer worksheet used during the Elaborate phase of the lesson is included.