| 1. | the senior officer of the U.S. Army or Air Force, a member of the Joint Chiefs of Staff, responsible to the secretary of a service branch. |
| 2. | (lowercase ) the senior or principal staff officer in a brigade or division or higher unit in the U.S. Army or Marine Corps, in a numbered unit in the U.S. Air Force, or in a unit in the U.S. Navy commanded by a rear admiral or one of higher rank. |
| 3. | (lowercase) the senior officer in command of a general staff, esp. that of the military forces of a nation. |
| 4. | (lowercase) the head of any staff: the chief of staff for the First Lady. |
| chief of staff n. pl. chiefs of staff Abbr. C. of S. or CS
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