Not a believer; in particular, not a member of a specific religious group(adjective)
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Use "nonbelieving" in a sentence
"The odds and gods are overwhelmingly against them, but ingenuity, perseverance and a peculiar kind of nonbelieving faith bring them through to a suitable, if not conventionally happy, ending."
"But both believing and nonbelieving scholars clearly can teach about religion in a secular setting without crossing the line into proselytizing."
"The headlines from a largely nonbelieving and predictably cynical world press were much as expected: ITALIAN SCIENTIST REPRODUCES SHROUD OF TURIN AND SCIENTIST PROVES SHROUD OF TURIN IS A MEDIEVAL FORGERY seemed to capture the general tenor of the stories going forth that afternoon from the conference room in Bologna."