LSJ
before a vowel προπέρυσιν, Adv.
two years ago, Pl. Euthd. 272b, D. 20.33, 33.25, PThead. 16.4 (iv AD), cj. in Lys. 9.4, etc. ; but πρωπέρυσιν is Att. acc. to A.D. Adv. 166.25, Phryn. PS p. 105 B., and is required by the metre in Pherecr. 182.
Liddell-Scott-Jones, Greek-English Lexicon (9th ed., 1940)
Pape
adv., vor zwei Jahren, Plat. Euthyd. 272b ; Lys. 9.4 ; Dem. 33.25 u. Folgde.
Pape, Griechisch-deutsches Handwörterbuch (3. Aufl., 1914)