n. A person who believes that no deities exist (especially, one who has no other religious belief).n. A person who rejects belief that any deities exist (whether or not that person believes that deities do not exist).n. A person who has no belief in any deities, such as a person who has no concept of deities.n. A person who does not believe in a particular deity (or any deity in a particular pantheon), notwithstanding that they may believe in another deity.adj. Of or relating to atheists or atheism; atheistic.