Origin of hā
c.1300, natural expression of surprise, distress, etc.; found in most European languages; in Old English, Greek, Latin, Old French as ha ha. A ha-ha (1712), from French, was "an obstacle interrupting one's way sharply and disagreeably;" so called because it "surprizes ... and makes one cry Ah! Ah!" [Alexander Le Blond, "The Theory and Practice of Gardening," 1712].