A noun meaning flood, deluge, or inundation — specifically used for the great Flood of Noah's day. The English word 'cataclysm' derives directly from this Greek word. It appears in Jesus's teaching about the end times, in Peter's reference to the Flood as a type, and in Matthew's parallel to the days of Noah.
The Flood narrative is one of Scripture's great theological anchors. Jesus uses kataklusmos to describe the days of Noah as a type of the coming judgment: people were eating, drinking, and marrying — normal life — until the flood came and swept them all away (Matthew 24:38-39). The lesson is not that normal life is sinful but that judgment can arrive without warning for those who are not prepared. Peter develops this further: the Flood is a type of final judgment by fire, and Noah's rescue through water is a type of baptism and salvation. The rainbow covenant means God will not repeat water judgment — but the fire is still coming.