Declare south-east to be hostile (6)
I believe the answer is:
averse
'be hostile' is the definition.
(I've seen this before)
'declare south-east' is the wordplay.
'declare' becomes 'aver' (averring is a kind of declaring).
'south east' becomes 'SE' (abbreviation).
'aver'+'se'='AVERSE'
'to' is the link.
(Other definitions for averse that I've seen before include "Strongly opposed (to something)" , "Disinclined, loath" , "Antipathetic" , "Disinclined, maybe to hard work" , "Not in favour of" .)