Which word describes a movement downwards?

The word "descent" specifically refers to the action or process of moving downward, which makes it the most fitting choice for describing a movement downwards. In various contexts, such as geography, aviation, or even metaphorical uses, "descent" clearly conveys the idea of going from a higher position to a lower one.

While "decline" may also imply a decrease or reduction in quality, quantity, or strength, it does not exclusively denote a movement downward and can relate to various contexts. On the other hand, "discrepancy" refers to a lack of compatibility or similarity between two or more facts, and "detain" pertains to the act of holding someone in custody or keeping them from proceeding, neither of which connect to the concept of downward movement. Therefore, "descent" is the most precise term for indicating downward movement.