atheist [atheists](a person who rejects belief that any deities exist, whether or not that person believes that deities do not exist) noun [UK: ˈeɪ.θiɪst] [US: ˈeɪ.θiəst]
nonbeliever(a person who does not believe, especially regarding religion) noun [UK: ˌnɑːn.bə.ˈliː.və(r)] [US: ˌnɑːn.bə.ˈliː.vər]