Businessman, a director, concealing lowest point (5)
I believe the answer is:
nadir
'lowest point' is the definition.
'businessman a director concealing' is the wordplay.
'concealing' indicates a hidden word.
'NADIR' is hidden in the letters of 'businessman a director'.
(Other definitions for nadir that I've seen before include "deep despair" , "Drain into the lowest point (5)" , "The lowest point of anything" , "lowest of the low" , "Low point" .)