When you want to describe something or someone in a negative way, you might use the phrase "casts a slur on." However, there are other synonyms you can use to avoid using the same expression repetitively. Some alternatives for "casts a slur on" include "tarnishes," "slanders," "smears," "defames," "discredits," "vilifies," and "besmirches." These words can add variety to your writing and help you avoid sounding repetitive. It's essential to choose the right word that accurately reflects the intended meaning and context, ensuring the language you use is appropriate and effective.