Definition of south-east:
(n) :
(chiefly UK) Alternative form of southeast. [The intercardinal compass point halfway between east and south; specifically at a bearing of 135°.]
(adj) :
(chiefly UK) Alternative form of southeast. [Of, in or pertaining to the southeast; southeastern.]
(adv) :
(chiefly UK) Alternative form of southeast. [Towards or in the direction of the southeast; southeastwards.]