The phrase "most calumniating" refers to something that is highly defamatory, slanderous, or libelous in nature. However, there are a number of antonyms that express the opposite sentiment. For example, instead of being "calumniating," one could be "commendatory," "praiseful," or "laudatory." Alternatively, the term could simply be "truthful," "honest," or "accurate." Regardless of the specific antonym chosen, the goal is to convey a sense of positivity or neutrality, rather than the negativity that is implied by the word "calumniating." By using these alternative terms, one can communicate more effectively and avoid causing harm or offense.