1. An older brother.
2. A man who assumes the role of an older brother, as by providing guidance or protection.
3. 1. also Big Brother An omnipresent, seemingly benevolent figure representing the oppressive control over individual lives exerted by an authoritarian government.
   2. A state, organization, or leader regarded in this manner.

[Sense 3, after Big Brother, a character in the novel 1984 by George Orwell.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.