What is the meaning of clear?

(DoD) To clear an engine; to open the throttle of an idling engine to free it from carbon.
(DoD) To clear the air to gain either temporary or permanent air superiority or control in a given sector.
(DoD) a. To operate a gun so as to unload it or make certain no ammunition remains; and b. to free a gun of stoppages.
(DoD) To pass a designated point, line, or object. The end of a column must pass the designated feature before the latter is cleared.
(DoD) To fly over an obstacle without touching it.
(DoD) To give a person a security clearance.
(DoD) To give one or more aircraft a clearance.
(DoD) To approve or authorize, or to obtain approval or authorization for: a. a person or persons with regard to their actions, movements, duties, etc.; b. an object or group of objects, as equipment or supplies, with regard to quality, quantity, purpose, movement, disposition, etc.; and c. a request, with regard to correctness of form, validity, etc.