Plural form of Mr (6)
I believe the answer is:
messrs
'plural form of mr' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for messrs that I've seen before include "Plural form of Mr - sounds untidy" , "Multiple men sounding sloppy" , "Multiple misters" , "Abbreviated misters" , "Form of address for a number of men" .)