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

• synchronized
• synchronized swimming
• synchronizer
• synchronizing
• synchronoscope
• synchronous
• synchronous converter
• synchronous motor
• synchronous operation
• synchronously
• synchrony
• synchroscope
• synchrotron
• Synchytriaceae
• Synchytrium
• Synchytrium endobioticum
• synclinal
• syncline
• syncopal
• syncopate
• syncopated
• syncopation
• syncopator
• syncope
• syncretic