Spanish for nothing, nada in Hemingway's "A Clean Well-Lighted Place" represents the author's understanding of nihilism, the belief that life is without objective meaning. Without any meaning in his life, the old man has attempted suicide, but has been saved by others. Now that he must endure life, the old man stay late at the cafe seeking light from the darkness of nothingness--nada--to which he must return. Thus, he shuns his return to the darkness because in it he is alone with his thoughts, his despair, his isolation. Because he knows that the world has no real norms, rules, or laws, it is only the light that keeps him from thinking about this nothingness.
Likewise, the older waiter recognizes the futility of a life that is essentially meaningless. So, he tries to keep the cafe open and light for those others like him. After the cafe closes, the waiter stops for a drink at another place because he, too, is reluctant to return to the nothingness that awaits him in the dark. "He would lie in the bed and finally, with daylight, he would go to sleep." Only the light makes him forget the nada.
The old man only says, "Nada," once, and he means it literally. The rest of the "nadas" come from the narration, which seems to be filtered through the old waiter's perspective:
It was all nothing, and a man was nothing, too...Some lived in it and never felt it but he knew it was nada y pues nada y pues nada. Our nada who art in nada nada be thy name thy kingdom nada they will be nada in nada as it is in nada. Give us this nada our daily nada and nada us our nada as we nada our nadas and nada us not into nada but deliver us from nada; pues nada. Hail nothing full of nothing, nothing is with thee...
Some have said this old waiter is the voice of the old man's soul. Maybe it is Hemingway's voice. But "nada" or "nothing" or "nothingness" is what the old man wants to escape by visiting the clean, well-lighted cafe.
Alone, with his nothingness, the old man suffers from insomnia: he cannot rest knowing his life has been lived unfulfilled. French existentialist Jean-Paul Sartre, who was influenced by Hemingway, says, in his famous work Being and Nothingness, that nothingness is total negation, a non-being, something that fails to exist by making choices.
So, the old man, through eyes of the old waiter, has ceased to exist. His life, his relationship with God, his relationships with men and women, his "Lord's Prayer" are all emptied of meaning. All he has now is monotony, routine, sleepless nights.
Nad in Hemingway's A Clean Well-Lighted Place refers to the nothingness that surrounds the old mans life. There is nothing in his life which was why he attempted to commit suicide. But he was cut down for the sake of saving his spirit, leading to the distrust of the institution of religion in the speech with the Lord's prayer being replaced by nada. Showing the meaninglessness of religion.