Brevity
There are a few possibilities for this:
'brevity' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for terseness that I've seen before include "Brevity" , "Abrupt quality" , "Abrupt manner" , "Short and concise expressiveness" , "Abruptness" .)
'brevity' is the definition.
(I've seen this before)
This is all the clue.
(Another definition for shortness that I've seen is " Brevity".)
'brevity' is the definition.
(thesaurus)
This is all the clue.