Lewis & Short

3. em, interj., = en (freq. in Plaut. and Ter. in best MSS.), Plaut. Merc. 2, 2, 42; id. Bacch. 4, 8, 29; id. Trin. prol. 3 (v. Brix ad loc.); id. ib. 1, 2, 148; id. Most. 5, 2, 58; id. Men. 2, 1, 26; id. Am. 2, 2, 146 Ussing ad loc.; Ter. Eun. 3, 2, 6 al., v. en.