The word 'causticness' refers to a harsh or corrosive quality in something or someone. Antonyms or opposite words for this term can include gentle, mild, benign, kind or amiable. These antonyms refer to qualities that are soft, tender and less abrasive. Other antonyms could be soothing, lenient, mellow or genial, meaning qualities that are agreeable and easy-going. These words are often used to describe pleasant experiences or people who are easy to be around. It is important to understand the opposite or antonyms of causticness to offer better communication, as alternating between different tone and language can alter emotions and bring about better results.