Border ran directly across mission (6)
I believe the answer is:
errand
'mission' is the definition.
(thesaurus)
'border ran directly across' is the wordplay.
'across' indicates the answer is hidden within the clue.
'ERRAND' is hidden in the letters of 'border ran directly'.
(Other definitions for errand that I've seen before include "Short commission" , "Short journey done for others" , "Native of a former German kingdom" , "Commission, task" , "Short delivery journey" .)