A game at cards.
“I left him at primero with the Duke of Suffolk.” —
... “Four cards were dealt to each player, the principal groups being flush, prime, and point Flush was the same as in `poker,' prime was one card of each suit, and point was reckoned as in `piquet.”' —Cyclopoedia of Games, p. 270.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Primero from Fact Monster: