Resembling or wearing a cap; also slang for something friendly or familiar, often used as a nickname or term of address.
From 'cap' combined with the informal diminutive suffix '-y'. Originally a nautical term for ship captains shortened in friendly speech.
In old nautical slang, sailors would call their captains 'cappy' as a term of respect mixed with camaraderie—it shows how working people create informal versions of official titles to feel closer to their leaders.
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