Complaints of free mason (5)
I believe the answer is:
moans
'complaints' is the definition.
(I have seen 'Trivial complaints ' mean 'moans' so perhaps 'complaints' could also mean 'moans')
'free mason' is the wordplay.
'free' indicates anagramming the letters.
'mason' is an anagram of 'MOANS'.
'of' acts as a link.
(Other definitions for moans that I've seen before include "Mournful sounds" , "Grumbles" , "Trivial complaints" , "Expressions of unhappiness" , "- - and groans" .)