The phrase "more matter of course" implies that something is expected or routine. However, there are many antonyms for this phrase that can convey a sense of surprise or disbelief. Some examples of antonyms for "more matter of course" include "unusual," "unexpected," "surprising," and "irregular." These words emphasize that something is not what is expected or typical, and can be used to add excitement or intrigue to a conversation or story. By using an antonym for "more matter of course," writers and speakers can make their language more vibrant and engaging.