Name of massacre, with safe gents maybe hiding below (8)
I believe the answer is:
peterloo
'gents maybe hiding below' is the definition.
I know nothing about this answer so I can't judge whether this works.
'name of massacre with safe' is the wordplay.
'name of massacre' becomes 'loo' (I can't justify this - if you can you should give a lot more credence to this answer).
'with' means one lot of letters go next to another.
'safe' becomes 'peter' (slang term for a safe).
'loo' after 'peter' is 'PETERLOO'.
Can you help me to learn more?
(Other definitions for peterloo that I've seen before include "massacre, say" , "Name given to Manchester massacre" , "1819 Manchester massacre scene" , "So-called massacre" , "Site of 1819 Manchester massacre" .)