ha (interj.) Look up ha at Dictionary.com
natural expression of surprise, distress, etc.; early 14c., found in most European languages (including Latin and Old French) but not in Old English (which did, however, have 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].