To say that a belief or ideas is nihilistic is to say that it radically depreciates what is perceived as having True value. For Friedrich Jacobi, who coined the term to defend the Transcendent, the rationalism of Kant’s critique was nihilistic, because it subverted man’s capacity to grasp, through faith, the Transcendent, and therefore, the otherworldly grounds of Value. For Nietzsche, who flipped the term to attack the idea of the Transcendent and attack the Faith, a clinging to the Transcendent was nihilistic, given Kant’s critique and European man’s post-Enlightenment situation, because it undermined man’s capacity to Bleibt der Erde treu, the naturel d’être, and, therefore, the very grounds for creating sacred values.
Both Jacobi and Nietzsche, of course, have been called Irrationalists, because, in their separate ways, both saw Rationalism, and the Cult of Reason, as nihilistic; for both, one simply cannot come to Value through reason alone, as many a man of the Enlightenment thought. For Jacobi, the highest value was given and to be understood; accordingly, the light of reason, with its conjured conceptual distinctions, was blinding. For Nietzsche, the highest value was created and to be birthed; accordingly, the light of reason, with its creativity dispeling dissections, was caustically bleaching.
For a brief discussion the concept of nihilism refer to Woolfolk (1990):
The idea of nihilista has been associated, for the most part, with two closely related but opposing theoretical approaches. The older approach has identified nihilism with the denial of either Christian faith or Platonic reason — in effect, with the negation of visions of a transcendent reality. Nihilism results from rejecting the idea of a suprasensible world standing metaphorically above or behind everyday existence. The first systematic theorist of this approach was the Bavarian philosopher of religion Franz von Baader (1970; Benz, 1949). During the twentieth century, it has continued in the writings of such varied theorists as Masaryk, Thielicke, Rosen, and most recently Allan Bloom, but its most profound, if equivocal, representative is still Dostoevsky….The second, younger — and today more prevalent — understanding of nihilism is closely linked to the name of Nietzsche, who was the first and most brilliant theorist to turn the idea of nihilista decisively against both Platonic reason and Christian faith. In contrast to theories that defend visions of a transcendent reality, nihilism’s origins are located in the acceptance rather than the rejection of such visions. The Nietzschean perspective has continued in different forms through Heidegger (1982) and Camus (1956), and may be readily identified in the work of many contemporary theorists such as Goudsblom (1980), Warren, and Schutte. (Other theorists, especially early sociologists such as Comte and Durkheim, and later Alfred Weber, represent more ambiguous middle positions that do not fall neatly into either camp.)…There are similarities in the two theoretical approaches, for at the heart of both is a vision of a desacralized world. By the term desacralized, I refer to a symbolic and experiential world in which, to use the deceptively simple formulation of both Dostoevsky and Nietzsche, “everything is permitted.” To know what is sacred is to know what is not to be done, nor even imagined. Such understandings of forbidden knowledge are stipulated in every culture. In a desacralized world, recognitions of what is not to be done would become apocryphal because they would either be lost, as in Dostoevsky’s vision, or revealed to be a fiction, as in the case of Nietzsche’s theory. Such a world in which “everything is permitted” may be impossible to realize, so perhaps it is best to leave the expression between quotes. But the premonition and image of a desacralized world is ineliminable from both perspectives. And as Max Weber knew, it is images of the world that have frequently acted as “switchmen” determining the tracks along which action has been pushed by ideal and material interests”