Friendly and familiar, or casual in a way that suggests companionship; British slang meaning like a friend or buddy.
From 'mate' (a friend or companion) plus the diminutive suffix '-y.' The word became popular in British English around the 1800s as informal, friendly speech.
Pirates probably didn't actually say 'matey' much—that's mostly a Victorian invention for stories, but the word stuck around in British slang because it captured something real about how sailors bonded as crew.
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