Vulgar leader shed some light on accession (6)
I believe the answer is:
afflux
'accession' is the definition.
(thesaurus)
'vulgar leader shed some light' is the wordplay.
I cannot quite understand how this works, but
'leader' could be 'f' (I have seen 'German leader ' mean 'f' so perhaps 'leader' could also mean 'f') and 'f' is found in the answer.
'some' could be 'a' and 'a' is found in the answer.
The remaining letters 'flux' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'on' is the link.
Can you help me to learn more?
(Another definition for afflux that I've seen is " A flowing towards (a point)".)