Something which is to be expected as following the natural course or order of things. "as a matter of course": naturally; without question, hesitation, or second thought. Also "as the matter of course" (rare).
Usually with hyphen. Occurring or following as a matter of course; that is to be expected. Of a person or a person's attitude: taking things as a matter of course; casual, offhand.
Late 16th century; earliest use found in Arthur Golding (d. 1606), translator. From matter + of + course.