We found 3 dictionaries that define the word lose one's marbles:

General (2 matching dictionaries)

1. lose one's marbles: Merriam-Webster
2. lose one's marbles: Wiktionary

Slang (1 matching dictionary)

3. lose one's marbles: English slang and colloquialisms used in the United Kingdom

Definitions from Wiktionary (lose one's marbles) ▸ verb:  Synonym of lose one's mind (“to become crazy”) ▸ Words similar to lose one's marbles ▸ Usage examples for lose one's marbles ▸ Idioms related to lose one's marbles ▸ Wikipedia articles (New!) ▸ Words that often appear near lose one's marbles ▸ Rhymes of lose one's marbles ▸ Invented words related to lose one's marbles