Head of company working a swindle (3)
I believe the answer is:
con
'a swindle' is the definition.
(con is a kind of swindle)
'head of company working' is the wordplay.
'head of' indicates taking the first letters.
'working' becomes 'on'.
The first letter of 'company' is 'c'.
'c'+'on'='CON'
(Other definitions for con that I've seen before include "Swindle; steer" , "Opposed" , "Peruse carefully or swindle" , "Study - swindle" , "Not in favour" .)