airhead · noun1
From air + head (“foremost, topmost, or leading part”), sense 1 (“area of hostile territory seized for use as an airbase”) by analogy with beachhead and bridgehead.
airhead · noun2
From air + head, in the sense of having one’s head filled with air instead of a brain; compare empty-headed.
Etymology from Wiktionary, CC BY-SA 4.0.