Thugs, a great many, around union (5)
I believe the answer is:
louts
'thugs' is the definition.
The answer and definition can be both people as well as being plural nouns.
Maybe you can see an association between them that I can't see?
'a great many around union' is the wordplay.
'a great many' becomes 'lots' (I've seen this in another clue).
'around' indicates putting letters inside.
'union' becomes 'U' (common abbreviation as in 'Trades Union Congress').
'lots' enclosing 'u' is 'LOUTS'.
Can you help me to learn more?
(Other definitions for louts that I've seen before include "Dolts" , "Yobs" , "Uncouth aggressive men" , "Coarse types" .)