chestnut, chess nut

Chestnut or chestnut ( one word ) means a large edible dark brown nut,  the tree it grows on, or its dark reddish brown color, often used to describe a horse--
We are saving these to make a chestnut cream filling for a cake.
"Under a spreading chestnut-tree The village smithy stands..."
She rode by on a chestnut mare.

Chestnut is also an old-fashioned term for an old or often-repeated joke or anecdote --
It's an old chestnut, but people still laugh at it.
That was an old chestnut when my grandfather first heard it.

Chess nut or chess nut ( two words, rhymes or nearly rhymes with chestnut ) means someone who is an enthusiast ( nut ) of the ancient game played on a board with 64 squares, by two people, with pieces of different rank ( chess ) --
He is a real chess nut; he hopes to be a Grandmaster some day.
He watches chess on TV; only a chess nut would do that.

Now that you know that, you can say --
"The old chess nut kept a chestnut in his pocket while he played; he thought it brought him luck."