English▸ exclamation used to represent the sound or effect of an explosion, gunshot, or blow (typically used in or associated with comic strips):
then kapow! the bomb detonates.
▪ used to convey the suddenness of an action or event:
Kapow! All your friends and family have suddenly been replaced with imposters.
– ORIGIN late 19th century (originally US, as kerpow): imitative.