Superstition, any excess of religion in general, following the ancient notion of paganism: one must be pious and guard oneself carefully against falling into superstition .

Religentem esse oportet, religiosum nefas. Aulus Gellius. I. IV. C. ix.  [1]

Essentially, superstition is a cult of religion, false, misguided, full of empty fears, contrary to reason as to all sane ideas that one ought to have of the Supreme Being. Or if you prefer, superstition is that form of enchantment, or magic power, that fear exercises over our soul; the wicked daughter of the imagination, it assaults the imagination with specters, dreams and visions; it is she, says Bacon, who has forged the idols of the vulgar, invisible genies, lucky and unlucky days, invisible signs of love and of hate. She attacks the mind, chiefly during illness or adversity; she overturns good discipline and venerable customs in favor of silly rituals and superficial ceremonies. Once she has planted deep roots in any religion at all, good or bad, she is able to extinguish the natural light and to perturb the healthiest heads. Finally, superstition is the most terrible scourge of humanity. Not even atheism itself (and this is saying a lot) destroys natural feelings, nor does it attack the laws or the mores of the people; but superstition is a despotic tyrant which forces everything to yield to its own chimeras. Its prejudices are superior to all other prejudices. An atheist takes an interest in civic peace, out of love of his own tranquility; but fanatical superstition , born of disordered imagination, overturns empires. See how the author of La Henriade [Voltaire] paints the sad effects of this dementia.

Ignorance and barbarism introduce superstition , hypocrisy maintains it with empty ceremonies, false zeal spreads it, and interest perpetuates it.

The hand of the monarch cannot too strongly reign in the monster that is superstition, for it is from this monster, much more so than from irreligion (always unpardonable) that the throne needs to fear for its authority and the country for its happiness.

Superstition in act constitutes fanaticism, properly speaking. See Fanaticism, which is one of the good and beautiful articles of the Encyclopédie .

1. ’Tis right to be religious, a crime to be superstitious.

2. Lorsqu'un mortel atrabilaire, / Nourri de superstition, / A, par cette affreuse chimère, / Corrompu sa religion, / Son ame alors est endurcie, / Sa raison s'enfuit obscurcie, / Rien n'a plus sur lui de pouvoir, / Sa justice est folle & cruelle, / Il est dénaturé par zele, / Et sacrilége par devoir.