1The middle of a course taken by a person or thing.
2A middle course or mode of procedure.
1Occurring or performed in the middle of a missile's course or a spacecraft's flight.
2US In extended use. Made, carried out, or performed during a course, project, campaign, etc.; frequently in "mid-course correction".
Early 16th century; earliest use found in Gavin Douglas (c1476–1522), poet and bishop of Dunkeld. From mid + course.