Board express crossing heart of Austria (4)
I believe the answer is:
stay
'board' is the definition.
(thesaurus)
'express crossing heart of austria' is the wordplay.
'express' becomes 'say' (I've seen this before).
'crossing' indicates putting letters inside.
'heart of' indicates the central letters.
The middle letter of 'austria' is 't'.
'say' placed around 't' is 'STAY'.
(Other definitions for stay that I've seen before include "Remain; detain" , "Postpone" , "Check" , "Reside" , "Supporting rod" .)