The antonyms for the word "credibleness" are untrustworthiness, incredibility, dubiousness, unreliability, and dishonesty. When someone or something lacks credibility, it means they are not believable or trustworthy. Such things often result in doubt, suspicion, and disbelief from others. It is important to have credibility in all aspects of life, especially in professional and personal relationships. Without it, one may face difficulty in establishing credibility and gaining trust. Therefore, it is crucial to ensure that you have credibility in your work, conduct, and interactions with others to maintain a positive reputation and avoid negative consequences.