Hit someone quickly with the palm of your hand, usually on the face, as a sign of anger or disrespect.
From Middle Dutch 'slappe' or similar Germanic sources. The origin is likely imitative—the word itself sounds like the action it describes.
Most onomatopoeia (sound-words) are obvious, but 'slap' is subtle—it doesn't just sound like a hit, the 'sl-' sound mimics the starting rush of motion before the impact.
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