Antonyms for the phrase "casts slur on" include clear, endorse, praise, honor, and commend. Clear implies that there is no suspicion of wrongdoing or negativity associated with an action or statement. Endorse suggests that one approves of and supports something, while praise connotes admiration and positive appraisal. Honor implies high respect and esteem, while commend indicates approval and recommendation. Using these antonyms allows for a more positive and encouraging tone when discussing a particular topic or individual. It is important to choose words carefully in order to communicate effectively and convey a desired tone or message.