lifer

noun Slang.

1. a person sentenced to or serving a term of life imprisonment.
2. a person committed to a professional lifetime career in the military.
3. a person who has devoted a lifetime to a profession, occupation, or pursuit.
4. (in birding)
   1. Also called life bird.a species of bird not seen previously and that will therefore be added to the bird watcher’s life list.
   2. the sighting of a bird of a previously unseen species: It seems like forever since I’ve had a lifer!

noun

1. informal a prisoner sentenced to life imprisonment

n.“prisoner serving a life sentence,” 1830, from life (n.).