Sky boss an idiot (7)
I believe the answer is:
airhead
'an idiot' is the definition.
(I've seen this before)
'sky boss' is the wordplay.
'sky' becomes 'air' (I've seen this before).
'boss' becomes 'head' (synonyms).
'air'+'head'='AIRHEAD'
(Other definitions for airhead that I've seen before include "Idiot" , "Bimbo" , "Numbskull" , "One not very bright" , "Dope" .)