Definition of lose one's marbles
- When he started ranting about how the government was out to get him, I thought he'd lost his marbles.
: to bring to destruction
: to miss from one's possession or from a customary or supposed place
: limestone that is more or less crystallized by metamorphism, that ranges from granular to compact in texture, that is capable of taking a high polish, and that is used especially in architecture and sculpture
: something (such as a piece of sculpture) composed of or made from marble
: something suggesting marble (as in hardness, coldness, or smoothness)
: to give a veined or mottled appearance to
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