Stonecutters (6)
I believe the answer is:
'stonecutters' is the definition.
('mason' can be a synonym of 'stonecutter')
This is the entire clue.
(Other definitions for masons that I've seen before include "Craftsmen working in stone" , "Stoneworkers - may be free" , "Workers with stone - may be Free" , "They work with stone and brick" .)