A high-ranking officer in the military or other uniformed services (1890s+ British)
Any high-ranking official; manager; chief; boss(1930s+)
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with brass-hat
A high-ranking official, as in All the brass bats were invited to the sales conference. The terms
big brass, top brass, and the brass all refer to high officials considered as a group. For example, John's one of the top brass in town—he's superintendent of schools. The origin of this term is disputed. Most authorities believe it originated in the late 19th-century British army, when senior officers had gold leaves on their cap brims. Another theory is that it referred to the cocked hat worn by Napoleon and his officers, which they folded and carried under the arm when indoors. In French these were called chapeaux à bras (“hats in arms”), a term the British are supposed to have anglicized as brass. By World War I brass hat referred to a high-ranking officer in Britain and America, and in World War II it was joined by the other brass phrases. After the war these terms began to be used for the top executives in business and other organizations.