1. Lacking sense or discretion
   "his rattlebrained crackpot ideas"
   - rattlepated, scatterbrained, scatty [Brit]

See also: foolish

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• tart
• tart up
• tartan
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• tartar steak
• tartare
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• Tartarean
• Tartarian honeysuckle
• tartaric
• tartaric acid
• Tartarus
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• tartlet
• tartly
• tartness
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• Tartuffe