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