The Collaborative International Dictionary of English v.0.48:
Southward \South"ward\ (?; colloq. ?), Southwards \South"wards\ (?; colloq. ?), adv. Toward the south, or toward a point nearer the south than the east or west point; as, to go southward. [1913 Webster]WordNet (r) 3.0 (2006):
southwards adv 1: toward the south; "the ship turned southerly" [syn: southerly, southward, southwards]