a-ha interj.

mid-15c., an expression of surprise, delight, disgust, or pain in nearly all Indo-European languages, but not found in Old English (where the equivalent expression was la!), so perhaps from Old French a "ah!, oh! woe!"

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).

expression of surprise or delighted discovery, late 14c.; see a-ha.