[adj] denying or questioning the tenets of especially a religion; "a skeptical approach to the nature of miracles"
incredulous, sceptical, skeptical, unbelieving
atheist, atheistic, creedless, faithless, heathen, heretical, incredulous, infidel, infidelic, irreligious, minimifidian, nonbelieving, nullifidian, pagan, questioning, quizzical, repudiative, skeptical, unbelieving, unchristian, unconfident, unconverted,