Boss tells Grant to leave (4)
I believe the answer is:
hugo
'boss' is the definition.
(designer Hugo Boss)
'tells grant to leave' is the wordplay.
I cannot really understand how this works, but
'leave' could be 'go' and 'go' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for hugo that I've seen before include "Victor maybe" , "Author of Les Miserables, d. 1885" , "Victor -; French author (Les Miserables)" , "Victor ---; --- Wolf" , "Man's name; sci-fi award" .)