The antonyms for the word "more matter-of-course" include unusual, extraordinary, exceptional, peculiar, different, and irregular. These words imply something that stands out from the norm or goes against established expectations. They suggest that whatever is being discussed is out of the ordinary or deviates from what is typically expected or accepted. For instance, someone might describe a particular behavior as peculiar if it is not what you would typically expect from that person. Similarly, the word exceptional implies that something is above and beyond what is considered ordinary or standard. When looking for the opposite of "more matter-of-course," these words can be helpful in describing anything that is not expected or typical.