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

• weakly
• weakly interacting massive particle
• weakness
• weal
• weald
• wealth
• wealthily
• wealthiness
• wealthy
• wealthy man
• wealthy person
• wean
• weaned
• weaning
• weanling
• weapon
• weapon of mass destruction
• weapon system
• weapon-grade plutonium
• weaponed
• weaponise
• weaponize
• weaponless
• weaponry
• weapons carrier