To physically attack one, as with punches and other blows, such that they suffer significant, life-threatening injury. This phrase can be used both literally and hyperbolically. Our neighbor is in the hospital because a burglar beat him to within an inch of his life. I'm worried that the captain of the football team will beat me to within an inch of my life if he finds out that I'm secretly seeing his girlfriend. If you ever scare me like that again, I'll beat you to within an inch of your life, I swear!