marble

marble /ˈmɑɚbəl/ noun
plural marbles
marble
/ˈmɑɚbəl/
noun
plural marbles
Britannica Dictionary definition of MARBLE
1 
[noncount] : a kind of stone that is often polished and used in buildings and statues — often used before another noun
2 
a  [count] : a little glass ball used in some children's games
b  marbles [noncount] : a children's game played with little glass balls

lose your marbles

informal + humorous
: to become insane