matter of life and death, a

matter of life and death

Something that is gravely serious. This top-secret project is a matter of life and death, so every bit of information in it needs to be accurate. I'm a nurse, so if I make a mistake at my job, it's a matter of life and death.
See also: and, death, life, matter, of

matter of life and death, a

A very urgent issue, situation, or circumstance. This expression can be used either literally, as in She told the doctor to hurry as it was a matter of life and death, or hyperbolically, as in Don't worry about finishing on time-it's hardly a matter of life and death. First recorded in 1849, it alludes to such urgency that someone's life depends on it. Although a matter of life or death would make more sense, it is rarely put that way.
See also: and, life, matter, of