Behave bravely or stoically when facing pain or a difficult situation, as in If they want to cut the budget deficit, they are going to have to bite the bullet and find new sources of revenue. This phrase is of military origin, but the precise allusion is uncertain. Some say it referred to the treatment of a wounded soldier without anesthesia, so that he would be asked to bite on a lead bullet during treatment. Also, Francis Grose's Dictionary of the Vulgar Tongue (1796) holds that grenadiers being disciplined with the cat-o'nine-tails would bite on a bullet to avoid crying out in pain.

To adjust to unpleasant circumstances: “The severe drought is forcing everybody to bite the bullet and use less water.” Before anesthesia, people undergoing surgery would bite on a bullet to help them withstand the pain.