"The sea nymph Calypso delayed Odysseus on her island Ogygia* for seven years." (American Heritage, 4e--my 5e is at home)
Her name comes from the Greek kaluptein 'to conceal' or 'to cover' presumably because that's what she did to Odysseus. (American Heritage doesn't know how Calypso music got its name. That is concealed to us.)
So, in Greek apo+kaluptein (the source of "apocalypse") means to uncover, or to reveal. So, Revelation is a calque (or loan translation, like Superman from Ubermensch) of the Greek, which referred, it would appear, to no more than the revealing of how the end times were going to go.
This is interesting to me because the "apocalypse" has a lot of rhetorical force today, and conjures images of rushing waves of flame and floods worthy of the name Diluvian, but it started out rather unassuming.
Here's an Amazon UK link to something called Apocalypse Calypso.
*Wikipedia says that Ogygia is also known as Atlantis, so there's a campaign angle.