1. Lacking sense or discretion
   - rattlebrained, rattlepated, scatty [Brit] 
2. Guided by whim and fancy
   - flighty, flyaway, head-in-the-clouds

See also: foolish, frivolous

• sublingual vein
• subliterary
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• subluxation
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• submandibular gland
• submandibular salivary gland
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• submaxillary
• submaxillary gland
• submaxillary salivary gland
• submediant
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