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

• partnership
• partnership certificate
• partridge
• partridge pea
• partridgeberry
• parts
• parts bin
• parts catalog
• parts catalogue
• parts department
• parts inventory
• partsong
• parttime
• parturiency
• parturient
• parturition
• partway
• party
• party boss
• party favor
• party favour
• party game
• party girl
• party line
• party liner