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

A.iota demonstrativum, in familiar Att. (not in Trag.), is attached to demonstr. Prons., to strengthen their force, and as it were point out the individual, as οὑτοσί, αὑτηΐ, τουτί, ἐκεινοσί, ὁδί, ταδί, τοσουτονί, τοσονδί, τυννουτοσί, etc.; also with the Particles γε δέ μέν inserted, as τουτογί, τουτοδί, ταυτηνδί, τῃδεδί, τουτουμενί, for τουτί γε, ταυτηνὶ δέ, etc.: also to demonstr. Advs., as οὑτωσί, ὡδί, ἐνθαδί, δευρί, νυνί, and νυνδί for νυνὶ δέ.—Of these forms, such as end in σί are sts. written in codd. with ν ἐφελκυστικόν before a vowel, as οὑτοσίν, ἐκεινοσίν, οὑτωσίν, etc.: such forms are recognized by A.D.Pron.59.24, 82.11, but are not found in best codd., e.g. of Pl. and D. [ι_ with the acute accent; along vowel or diphthong before it is shortd., as αὑτη^ί, οὑτοι^ί.]