To hit quickly and sharply with the palm of the hand or a flat object.
From Middle Dutch 'slappen' or Middle Low German 'slappen,' imitative of the sound made by the action. The word is onomatopoeic, directly representing the sharp sound of the impact.
As an onomatopoeia, 'slap' is one of those perfect words where sound matches meaning - you can almost hear the action in the word itself. Across languages, words for slapping tend to be remarkably similar because they all try to capture that distinctive sharp sound.
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