LSJ
(δῆμθε before a consonant, Bato 7.3), indef. Adv. = δήπου, chiefly used before a vowel (before a consonant, Pl. Ion 534a, etc.), freq. in Com., Ar. V. 296, Pl. 140, etc. ; in answer to a rhetorical question, οὐ δ., ἀλλά… Lys. 6.36, cf. D. 27.59, Pl. Phlb. 62e, etc.
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)
Pape
= δήπου, bes. vor Vokalen, Lys. 6.36 ; Isae. 7.32 ; Plat. Phil. 62e. Auch δήπουθε, Bato com. Stob. fl. 6.29.
Pape, Griechisch-deutsches Handwörterbuch (3. Aufl., 1914)