Round Table title (3)
I believe the answer is:
sir
'round table title' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sir that I've seen before include "Noble title of undesirable kind" , "Title given to 10 Across" , "Gentleman's form of address" , "Formal and deferential address to a man" , "Title of 1 across" .)