Summon up one's strength to face unpleasantness or overcome a difficulty. For example, Gritting his teeth, he dove into the icy water. This expression uses grit in the sense of both clamping one's teeth together and grinding them with effort. [Late 1700s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.