Heading for border (5)
I believe the answer is:
bound
This could be a double definition.
'heading' is the first definition.
The answer and definition can be both locations as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'for border' is the second definition.
(synonyms)
Can you help me to learn more?
(Other definitions for bound that I've seen before include "demarcation" , "vault" , "Certain - fastened" , "books are" , "Jump - certain - limit" .)