adj

• (rare, archaic) Proceeding from, or appointed by, fate or destiny.
  "She mixed furniture with the same fatal profligacy as she mixed drinks, and this outrageous contact between things which were intended by Nature to be kept poles apart gave her an inexpressible thrill."
• (rare, archaic) Foreboding death or great disaster.
  "Such a scandal as the prosecution of a brother for forgery—with a verdict of guilty—is a most truly horrible, deplorable, fatal thing. It takes the respectability out of a family perhaps at a critical moment, when the family is just assuming the robes of respectability: […] it is a black spot which all the soaps ever advertised could never wash off."
• (computing) Causing a sudden end to the running of a program.
  "a fatal error; a fatal exception"

noun

• (computing) A fatal error; a failure that causes a program to terminate.