Business bigwig, for short (4)
'business bigwig for short' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for exec that I've seen before include "Board member" , "CEO?" , "Businessman" , "Senior businessperson (abbr)" , "Business leader" .)
(Other definitions for ceo that I've seen before include "Initials commonly used for top boss" , "Initially, the top boss" , "Initially, top man in an organisation" .)