1. a person who is eccentric, foolish, or mentally unstable
Usage: archaic or informal; often used as a mild insult

1. eccentric, foolish, or mentally unbalanced
Usage: archaic or informal

Examples

• He was dismissed as a crackbrain by his colleagues for proposing such an unusual theory.
• Her crackbrain ideas often amused rather than impressed the board members.
• The old crackbrain spent his days muttering to himself on the park bench.
• Some thought his inventions were the work of a crackbrain, but a few recognized his genius.
• That crackbrain scheme will never work in practice.
• The village crackbrain was known for his wild stories and strange behavior.