From The Collaborative International Dictionary of English v.0.48 :
airhead \air"head`\ ([^a]r" h[e^]d`), n.
an airheaded person. [disparaging]
[PJC]
From WordNet (r) 2.0 :
airhead
n 1: a flighty scatterbrained simpleton; "she's a total airhead";
"every airhead on a big salary rushed out to buy one"
2: a bridgehead seized by airborne troops