The word "ructious" is not a commonly used term in the English language, and therefore doesn't have any widely recognized antonyms. However, the word is often associated with loud and chaotic behavior, and antonyms that could be used to describe the opposite of ructious could include words like peaceful, serene, calm, harmonious or tranquil. These words would be used to describe situations where there is no commotion, and things are quiet, relaxed and well-ordered. Conversely, ructious behavior could be described with antonyms like orderly, disciplined, or controlled, indicating a lack of chaos or disturbance. So while there may not be specific antonyms for the word "ructious," there are certainly words that can be used to describe its opposite.