1. 
[syn: airheaded, dizzy, empty-headed, featherbrained, giddy, light-headed, lightheaded, silly]
The Collaborative International Dictionary of English v.0.48:
empty-headed \empty-headed\ adj.
   lacking seriousness; given to frivolity.
   Syn: airheaded, dizzy, featherbrained, giddy, lightheaded,
        light-headed, silly.
        [WordNet 1.5]
WordNet (r) 3.0 (2006):
empty-headed
    adj 1: lacking seriousness; given to frivolity; "a dizzy
           blonde"; "light-headed teenagers"; "silly giggles" [syn:
           airheaded, dizzy, empty-headed, featherbrained,
           giddy, light-headed, lightheaded, silly]