The words that are antonyms of "speak highly of" are "disparage", "criticize", "belittle", and "deprecate". These words convey negative connotations, indicating that something or someone is not worthy of praise or commendation. When one disparages, they are intentionally speaking ill of a person or thing, harming their reputation. To criticize someone or something shows flaws or drawbacks, highlighting negative aspects. Belittling or deprecating someone is to lower their worth or make them feel inferior. Therefore, it is important to consider using positive language and uplifting words to describe people and things around us.