Most words as ostentatiously Latinate as superstition have transparent etymologies: election is from e(x)- ‘out of’ + legere ‘to choose,’ conflagration is con- ‘with, together’ + flagrāre ‘to burn,’ and so on. But superstition is different: its formation is equally transparent, super- ‘above’ + stāre ‘to stand,’ but what does that have to do with the meaning “Religious belief or practice considered to be irrational, unfounded, or based on fear or ignorance; excessively credulous belief in and reverence for the supernatural” (to quote the OED)? Today it occurred to me to see if the OED entry had been updated, and indeed it has, less than two years ago (June 2012), so their etymology is presumably the latest word on the subject; it turns out to be an old problem, and the Romans themselves wondered about it:
The semantic motivation for the word is unclear. The classical Latin author Cicero suggested (Natura Deorum 2. 28. 72) that superstitious people (superstitiōsī) were so called because they practised excessive religious devotion in order that their children might survive (superstites essent), but this is probably a folk etymology. A view held in late antiquity is that the use of the words superstitiō ‘superstition’ and superstitiōsus ‘superstitious’ with reference to religion derives from the idea that such practices were superfluous or redundant. Compare Isidore Origines 8. 3. 6 Superstitio dicta eo quod sit superflua aut superinstituta observatio ‘Superstition is so called because it is the name for redundant and superseded (religious) observation’. Classical Latin superstes was used with reference to a soldier standing over the prostrate body of a defeated enemy, and it has also been suggested that from this use, classical Latin superstitiō had the sense ‘superiority’, and hence developed the senses ‘prophecy’ and ‘sorcery’.
The Oxford Latin Dictionary, now several decades old, says “orig. sense perh. ‘state of religious exaltation.’” We’ll never know for sure, but I thought people might be interested in the current educated guesses.