The Greek verb asebeo (ἀσεβέω) means "to be ungodly, to act impiously, to live without reverence for God" — from asebeia (H763). It describes the active practice of ungodliness, the living out of a godless orientation in concrete behavior.
The verb asebeo appears in 2 Peter 2:6 where Peter describes how God condemned Sodom and Gomorrah as an example of what will happen to the ungodly — specifically, those who "live ungodly lives" (asebesin). Jude 1:15 uses the term four times in a single verse to emphasize the comprehensive scope of judgment against those who have "acted impiously." The concentration of the term underscores the severity with which God views the deliberate, willful rejection of His lordship. The antidote is eusebeia — godliness cultivated through the knowledge of Christ (2 Peter 1:3).