Terrible leader in government over the border (4)
I believe the answer is:
grim
'terrible' is the definition.
(thesaurus)
'leader in government over the border' is the wordplay.
'leader in' indicates taking the first letters.
'over' says to put letters next to each other.
'the border' becomes 'rim' (I've seen this before).
The first letter of 'government' is 'g'.
'g'+'rim'='GRIM'
(Other definitions for grim that I've seen before include "Stern and unsmiling" , "Tight-lipped and foreboding" , "Harsh and merciless" , "Dreadful" , "Resolute" .)