Lewis & Short

ĕhem, interj., an exclamation of joyful surprise, ha! what! ehem, optume! quam dudum tu advenisti? Plaut. As. 2, 4, 43; id. Most. 3, 2, 38; id. Mil. 4, 9, 5; id. Rud. 3, 5, 25; Ter. And. 2, 5, 6: ehem, pater me, tu hic eras? id. Eun. 1, 2, 6; 3, 2, 9; id. Ad. 1, 2, 1; App. M. 2, p. 124, 29.