The phrase "on the descendant" is often used to describe something that is decreasing or declining. There are many synonyms for this phrase that can be used to convey a similar meaning. For example, "on the decline," "on the wane," "sliding," "diminishing," "falling," "receding," and "waning" are all useful synonyms for this phrase. Other phrases that can be used to describe a downward trend include "losing ground," "going down," and "dropping off." Synonyms can be a great way to add variety and nuance to your writing, so consider incorporating some of these options to make your language more creative and engaging.