The etymology of the word is often understood as "lacking worth", from two common words: beli- (בְּלִי "without-") and ya'al ( יָעַל "to be of value").
Image: 'Enter Scorpius' by Al Wiggins Jr.
Their king is the angel from the bottomless pit; his name in Hebrew is Abaddon, and in Greek, Apollyon —the Destroyer. Apocalypse 9:11 (NLT)