Apocalypse originally meant an uncovering (by the gods), a revelation of things heavenly and godly.
Here, also, is the etymology of another word, Armageddon (I think):
I believe Megiddo was the town atop a hill (Har) in which lived many jews. In a particular period, the Romans came to conquer this town; with the thought of slavery, came the thought of suicide; and thus they comported themselves in accord with this latter sentiment, and concomitant to this malefaction was even the murder, or assisted suicide, of their progeny, the flesh of their flesh.
Thus, to the people, the bloody scene at the Har, Meggido, (the hill, Meggido; Armageddon) was the quintessence of the brutality and vehemency, with which the end of the world they supposed would come.
P.S. Sorry for the attempted drama. I wanted a narrative and unusually animated nuance for my exegesis of sorts...