:)
In the Internet sense of the word, the trolls in question live under bridges and spring out to surprise those who would cross with unpleasant demands and behaviour. Not cave-dwellers at all.
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Hey, this is Hacker News, if we can't bikeshed the etymology of "troll," what use is this medium?
"The term is used to denote various beings, such as a jötunn or mountain-dweller, a witch, an abnormally strong or large or ugly person, an evil spirit, a ghost, a blámaðr, a magical boar, a heathen demi-god, a demon, a brunnmigi, or a berserker."
I think that over time, and thanks to various "fairy tales," we have settled on Trolls as he mountain/riock/cave-dwellers who are turned to stone if exposed to sunlight.
Sadly, the Internet Troll multiplies when given attention. Sunlight does not disinfect social media.