1. Guided by whim and fancy
   "flighty young girls";
   - flyaway, head-in-the-clouds [informal], scatterbrained, dippy [informal]
    
2. Unpredictably excitable (especially of horses)
   "The flighty colt was difficult to train";
   - skittish, spooky [N. Amer, informal], nervous, skittery

Derived forms: flightier, flightiest

See also: ditsy [N. Amer, informal], ditzy [N. Amer, informal], excitable, frivolous