Which of the following best defines the word "wax"?

The word "wax" in this context is used to mean "to become larger or increase in size." This definition is often associated with the natural process of the moon phases, where the moon is described as "waxing" when it moves from new to full, indicating an increase in illumination.

The concept of growth or expansion is central to the meaning of "wax" when used in various contexts, such as in expressions like "waxing lyrical," which refers to speaking in an increasingly positive or elaborate manner. Therefore, the choice that states "to become larger" accurately captures this essence of the word.