Sneers set somehow to lead to an abrupt manner (9)
I believe the answer is:
terseness
'an abrupt manner' is the definition.
(I've seen this before)
'sneers set somehow' is the wordplay.
'somehow' is an anagram indicator.
'sneers'+'set'='sneersset'
'sneersset' with letters rearranged gives 'TERSENESS'.
'to lead to' is the link.
(Other definitions for terseness that I've seen before include "Brevity" , "Short and concise expressiveness" , "Abrupt quality" , "Abrupt manner" , "Abruptness" .)