The antonyms for the word "acted as witness" are quite a few. Some of the antonyms for the phrase are denied knowledge, concealed truth, ignored, repudiated, neglected, or disregarded. These words mean that one did not testify to the truth or did not take up the responsibility to testify at all. They suggest a failure to report, lack of credibility or even moral and ethical failures. The importance of acting as a witness cannot be overemphasized. By testifying to the truth, individuals ensure that justice is served, and the truth can prevail. So, it is vital to recognize these antonyms and the implications they bring about, to avoid them in any situation requiring truth telling.