A sensation on the skin that makes you want to scratch; or a strong desire or urge to do something.
From Old English 'giccan' or related Germanic roots, possibly imitative in origin. The word has remained relatively unchanged since Anglo-Saxon times, suggesting it describes a very basic human sensation.
The word is probably onomatopoeia—it might imitate the sound or feeling of scratching itself! And we use it metaphorically for any strong urge: 'seven-year itch,' 'wanderlust itch'—the physical sensation became emotional.
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