Ah, you destroyer, who yourself have not been destroyed, you traitor, whom none has betrayed! When you have ceased to destroy, you will be destroyed; and when you have finished betraying, they will betray you. - Isaiah 33:1 (ESV)
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").
A worthless person, a wicked man, goes about with crooked speech, winks with his eyes, signals with his feet, points with his finger, with perverted heart devises evil, continually sowing discord; therefore calamity will come upon him suddenly; in a moment he will be broken beyond healing. - Proverbs 6:12-15 (ESV)