Title usually abbreviated (6)
I believe the answer is:
mister
'title usually abbreviated' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for mister that I've seen before include "that's what you'd call him" , "Form of address to a man, used without his name" , "Set rim (anag.)" , "Mr" , "Bloke" .)