Declivous, a rare and seldom-used word, describes something that slopes or inclines downwards. Therefore, its antonyms, which describe things that ascend or incline upwards, would be terms like, ascending, climbing, mounting, and rising. Other antonyms that can be used to describe things that are not sloping downwards include level, horizontal, even, flat, and upright. It is crucial to understand antonyms as they help to expand our vocabulary, improve the ability to express ourselves effectively in writing and speaking, and facilitate better communication. Using antonyms also provides a certain level of textual variety by ensuring that we are not relying on the same terms to describe the same actions.