Leave to show the trade union president (6)
I believe the answer is:
depart
'leave to show' is the definition.
I can't judge whether this defines the answer.
'trade union president' is the wordplay.
I cannot really see how this works, but
'president' could be 'p' (common abbreviation eg in VP) and 'p' is located in the answer.
an anagram of 'trade' is 'deart' which is within the left over letters.
No letters remain.
This explanation may well be incorrect...
'the' acts as a link.
Can you help me to learn more?
(Other definitions for depart that I've seen before include "Prated (anag.)" , "21" , "Go away; deviate" , "Stray" , "Quit" .)