Oner

The winner was the last to flick a marble into the gully. A oner had to beat a fourer four times to win, a fourer had to beat a twelver three times, and so on.

May all your conkers be oners / May your love life fail with dishonours

The history of 'oners' becoming 'sixers' through successive victories[…]

Conkers so highly prized that it's a wonder they even manage to hit the ground before being swept away to be pickled or baked and then going on to new careers as 'oners', 'twoers', and so forth.