Lewis & Short

Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.

1. ai, in old Lat., corresponding to ae: AIDILIS, CAISAR, AITERNOS, for Aedilis, Caesar, aeternus; also, still later, sometimes in the poets in the termination of the genitive of the first decl.; but, as in Enn. and Lucr., per diaeresin always dissyl. with long penult: furit intus aquāï, Verg. A. 7, 464: aurāï simplicis ignem, id. ib. 6, 747: terrāï frugiferāï, Mart. 11, 91, 5; cf. Quint. 1, 7, 18; Spauld. Prisc. 728; Prob. 1438; Vel. Long. 2222; Mart. Vict. 2460 P.
In prim. syllables, as in voc. Gaĭ, ăi could not be changed to ae if i was an ending; but i was changed to i cons., when the word received accession, e. g. Gaius.
When a conson. followed ai, as in CNAIVOS for ΓΝΑΙϝΟΣ (v. the Epitaphs of the Scipios, in the Append.), ae was written at a later per., as Gnaeus; hence from Γράϊος both Graecus and Graius; from Αἴακος, Aeacus, and Aiax, for Αἴας, were formed; just as Achaeus or Achivus with Achaĭus or Achaĭcus was used.

    1. 2. * ai = αἴ, interj., denoting grief, ah! alas! Ov. M. 10, 215.

3. ai, imper., from aio.