To wane means to:

To wane refers to a gradual decline or decrease, particularly in terms of visibility or intensity. This term is often used in the context of the moon, where the visible portion diminishes after a full moon. Therefore, the idea of decreasing in phase accurately captures the essence of the word. This can apply to other contexts as well, such as emotions or trends, where a certain strength or presence diminishes over time. The other choices indicate an increase, constancy, or expansion, which do not accurately reflect the meaning of wane.