What is the action of expressing disapproval of something?

The action of expressing disapproval of something is best captured by the term discountenance. This term specifically refers to the act of showing disapproval or discouragement towards a certain behavior, action, or situation. It suggests a strong stance against something that is seen as undesirable or inappropriate.

In contrast, the other terms imply positive actions or support. Approve suggests agreement or endorsement, while encourage and support connote a sense of promoting or uplifting a particular idea or action. Therefore, discountenance stands out as the correct choice because it directly aligns with the concept of expressing disapproval.