Distant impasse is ending in clash (11)
I believe the answer is:
standoffish
'distant' is the definition.
(thesaurus)
'impasse is ending in clash' is the wordplay.
'impasse' becomes 'standoff' (I've seen this before).
'ending in' indicates one should take the final letters.
The last letter of 'clash' is 'h'.
'standoff'+'is'+'h'='STANDOFFISH'
(Other definitions for standoffish that I've seen before include "Unfriendly" , "Reserved, aloof" , "Cold" , "Distant" , "like a half of rugby?" .)