real McCoy

Etymology
Corruption of, this latter attested in 1856 as “A drappie o’ the real MacKay” (A drop of the real MacKay). How “MacKay” became “McCoy” is unclear; first attested in the form “McCoy” in the US in 1908.

The term is the subject of many folk etymologies, discussed at the Wikipedia entry.

Noun

 * 1)  The genuine thing, neither a substitute nor an imitation.

Translations

 * Polish: