Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Perseus.
1. ĕī, dat. of is, q. v.
2. ei, interj., oh! etc., Plaut. Cas. 3, 6, 7; Ter. And. 1, 1, 46, v. hei.
hei (also ei), interj., an exclamation of grief or fear, ah! woe! freq. joined with mihi, ah me! woe is me! hei, perii miser! Plaut. Am. 2, 2, 36: hei, occidi! id. Aul. 2, 1, 28: hei, non placet convivium! id. Amph. 2, 2, 173: hei, vereor, ne quid Andria apportet mali, Ter. And. 1, 1, 46: hei, metuo lenonem ne, etc., id. Phorm. 3, 2, 6: hei, video uxorem, id. ib. 5, 3, 14 ei mihi, qualis erat! Enn. ap. Serv. ad Verg. A. 2, 274; imitated by Verg. A. 2, 274: hei mihi, perii hercle! Plaut. Aul. 2, 8, 21: Am. Hei mihi! Br. Ne pave, id. Amph. 5, 1, 57: hei mihi, vereor dicere! Ter. And. 2, 1, 22: hei mihi, quantum Praesidium Ausonia et quantum tu perdis, Iule! Verg. A. 11, 57: hei mihi! conclamat, Ov. M. 6, 227: hei mihi! hei mihi! istaec illum perdidit assentatio, Plaut. Bacch. 3, 3, 7: hei misero mihi! id. Aul. 2, 2, 23; Ter. Heaut. 2, 2, 5. id. Ad. 2, 1, 19.