The numinous is a term coined by the German theologian Rudolf Otto in his 1917 book Das Heilige, translated into English as The Idea of the Holy, to name a distinctive category of religious experience Otto argued could not be reduced to ordinary moral or rational feeling. Otto described the numinous through the Latin phrase mysterium tremendum et fascinans, a mystery that is at once tremendum, provoking awe, dread and a sense of overwhelming power before which the self feels creaturely and small, and fascinans, simultaneously and paradoxically drawing the person toward it with a compelling fascination, so that the experience combines terror and attraction rather than being simply one or the other.
Otto held that this numinous quality was the primary, non-rational core of religious experience underlying and prior to any specific doctrinal or ethical content a tradition later builds around it, describing God or the sacred, in this experiential register, as wholly other, categorically different from any ordinary object of human experience or thought rather than merely a greater version of familiar things. Otto drew his supporting examples from a wide range of religious literature beyond his own Lutheran background, arguing that the tremendum and fascinans he described could be located, in varying intensity, within Jewish, Islamic and Indian religious texts as well as Christian ones, part of what made the category read as comparative rather than confined to one tradition.