marbles.

Any of several children's games played with small balls (made of marble or more commonly glass).

Egyptian boys played marbles before the days of Moses.

Sanity.

Grandpa's lost his marbles, but at least he still recognizes us.

Granny's still got all her marbles.

Bits of rolled-up rubber shed by the tires of race cars that accumulate at the edges of the track, especially at the corners.

plural of marble

Marbles were among the treasures found buried in the ruins of Pompeii.

third-person singular simple present indicative of marble