There's a lot of folk etymology touted around in religion, as in other places.
The word God apparently comes from a proto-Indo-European root meaning 'to invoke' or 'to offer sacrifice', whereas good comes from a root of about the same age meaning 'fitting, pleasing, belonging together'. It's often claimed that they're related, and certainly in goodbye one has been corrupted into the other, but the connection is spurious.
Devil is interesting: from the Greek diabolos, which literally means 'to throw across' but has the general meaning of 'to slander'. Satan comes from hebrew ha-Satan, 'the accuser'. The original function of Satan, as a being who torments humans to test their faith at the direct command of God (not a very comfortable idea for later writers!), is pretty clear from the book of Job, the oldest book in the OT.
There are a couple of other interesting 'word origins' I like. The fruit of the garden of Eden, which is not named in Genesis, is in art and popular culture generally assumed to be an apple. This is because medieval scholars thought there was a connection between the Latin words malum, evil, and malus, apple.
And, in the Malleus Maleficarum of 1487 - a German handbook for witch-hunters, which had a total obsession with the evilness and depravity of women - the Latin word for woman, femina, was nonsensically supposed to be derived from fe, faith, and minus, less, because women of course had less faith than men.
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"Grunge? Isn't that some gross shade of greenish orange?"