Katakaiō (κατακαίω, G2618) means to burn down, to burn up completely, to consume entirely with fire. From kata (intensifier — completely) + kaiō (to burn/set on fire). The prefix kata gives the sense of thoroughness — not just burning but burning down to nothing. Appears in Matthew 3:12; 13:30,40; Luke 3:17; Acts 19:19; 1 Corinthians 3:15; Hebrews 13:11; Revelation 8:7; 17:16; 18:8.
John the Baptist introduces katakaiō in Matthew 3:12: 'He will clear his threshing floor, gathering his wheat into the barn and burning up (katakausei) the chaff with unquenchable fire.' The complete burning implied by the kata- prefix is theologically intentional: chaff is not partially destroyed or put aside — it is utterly consumed. This fire of judgment is the inverse of the fire of purification (1 Peter 1:7). In Acts 19:19, new converts at Ephesus burned their sorcery scrolls publicly — katakaiō as decisive break with the past, spiritual warfare made visible. 1 Corinthians 3:15 uses it for the eschatological testing of a believer's works: 'if it is burned up (katakaesetai), the builder will suffer loss but yet will be saved — even though only as one escaping through the flames.' Katakaiō is both judgment and purification — the fire that destroys what is not of God and refines what remains.