Bite the bullet
Meaning
Endure pain with fortitude.
Origin
In the days before effective anesthetics soldiers were given bullets to bite on to help them endure pain. Improvements in battlefield medicine has seen the real act of biting bullets migrated into metaphor, although it must still happen occasionally.
First recorded in print in Kipling's 'Light that Failed', 1891. Kilpling uses 'bite the bullet' rather than 'bite this bullet', which we might have expected if the idea were new to the character being spoken to. That tends to suggest the phrase was already public when the story was written.