i. The distance between two given meridians measured along a standard parallel and expressed in nautical miles. It is the east-west component of the rhumb-line distance between two points. The value of departure between two meridians decreases with increasing latitudes, and vice versa. Departure in nautical miles = change of longitude in minutes × cosine mean latitude.
ii. The distance traveled in an east to west direction between two points.
iii. Aircraft taking off from an airport under departure control.
iv. Aeroelastic instability that may exist in roll, pitch, or yaw. Aircraft may break up during an aereoelastic departure. It is a situation in which there is an uncommanded increase in the angle of attack (a) and consequent loss of control. It is a form of aerodynamic departure as in a pitch-up.
v. The action or event of an aircraft leaving a place, as in “5 departures, 2 arrivals.”

Aviation dictionary. 2014.