εἰ

• αἰ (ai) – Doric, Epic
• εἴ (eí) – stressed
• εἰκ (eik) – before a word starting with a vowel

From Proto-Indo-European *éy. See its sense, “that”, in ἐπεί (epeí) and compare the history of Latin sī.

εἰ • (ei)

1. if

• εἰ in Liddell & Scott (1940) A Greek–English Lexicon, Oxford: Clarendon Press
• εἰ in Liddell & Scott (1889) An Intermediate Greek–English Lexicon, New York: Harper & Brothers
• εἰ in Autenrieth, Georg (1891) A Homeric Dictionary for Schools and Colleges, New York: Harper and Brothers
• εἰ in Bailly, Anatole (1935) Le Grand Bailly: Dictionnaire grec-français, Paris: Hachette
• εἰ in Cunliffe, Richard J. (1924) A Lexicon of the Homeric Dialect: Expanded Edition, Norman: University of Oklahoma Press, published 1963
• εἰ in the Diccionario Griego–Español en línea (2006–2019)
• εἰ in Slater, William J. (1969) Lexicon to Pindar, Berlin: Walter de Gruyter
• G1509 in Strong’s Exhaustive Concordance to the Bible, 1979
• εἰ in Trapp, Erich, et al. (1994–2007) Lexikon zur byzantinischen Gräzität besonders des 9.-12. Jahrhunderts [the Lexicon of Byzantine Hellenism, Particularly the 9th–12th Centuries], Verlag der Österreichischen Akademie der Wissenschaften
• Woodhouse, S. C. (1910) English–Greek Dictionary: A Vocabulary of the Attic Language‎, London: Routledge & Kegan Paul Limited.
  • assuming idem, page 47.
  • grievance idem, page 373.
  • if idem, page 414.
  • intestate idem, page 453.
  • open idem, page 574.
  • spurn idem, page 806.
  • supposing idem, page 841.
  • whether idem, page 975.
  • would that idem, page 991.