In report gloss over mutual-aid organisation (5)
I believe the answer is:
guild
'organisation' is the definition.
(guild is a kind of organization)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for guild that I've seen before include "Group of craftsmen" , "Trade union" , "Alliance" , "corporation" , "Medieval association of merchants" .)