1. A belief in the magical effects of a specific action or ritual, especially in the likelihood that good or bad luck will result from performing it: Virginia's sister lives in a high-rise housing complex that doesn't have the 13th floor due to the superstition that it would bring misfortune!
2. An irrational, credulous, and unfounded belief in dark and unearthly creatures or beings: Greg thought that the ghost stories his sister was reading were based on pure superstition!
3. Etymology: via French from Latin superstition; superstes, "standing over (in awe)"; from super, "over, above" plus stare, "to stand".

Defined by some as, "the unreasoning fear of anything founded on the fear of the unreasoning."