Henry George Liddell, Robert Scott, A Greek-English Lexicon

0-0.The ι 'subscript' of modern texts was said προσγράφεσθαι, cf. D.T.639.14, A.D.Pron.87.10, Ael.Dion.Fr.192 (also τὸ ληιστής (disyll.) . . ἔχει προσκείμενον τὸ ι_ Hdn.Gr.2.946), and this mode of writing is found in Papyri, Inscrr., and some medieval Mss. (e.g. cod. A of Plato, saec. ix, which has τῶι = τῷ, etc.); the present mode is found as early as the tenth century, and came into use in the thirteenth. This ι was prob. always pronounced up to ca. 150 B.C., but thereafter dropped in pronunciation, cf. D.T. l.c.; hence called “ι ἀνεκφώνητον” Choerob.in Theod.1.143 and freq. omitted in Pap. and Inscrr. (cf. Epigr. ap. Str.14.1.41,= SIG766), later freq. restored in writing, sts. in the wrong place (v. ῥάθυμος). From ca. 150 B.C. (at Argos from ca. 450 B.C., v. SIG56.13) ει was pronounced ι and the sound is written indifferently ει or ι.