Put up with the worst of some bad circumstance, as in It was the secretary who had to bear the brunt of the doctor's anger. This idiom uses brunt in the sense of “the main force of an enemy's attack,” which was sustained by the front lines of the defenders. [Second half of 1700s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.