Scatterbrain (7)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">scatterbrain</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for airhead that I've seen before include "Stupid person" , "Vacuous person" , "clown" , "Fool" , "one with a small brain" .)
(Other definitions for space cadet that I've seen before include "one who often gets high" , "trainee astronaut" , "one high on drugs" .)