What is the meaning of εἶ?

Old name of the letter ε (epsilon, see ἒ ψιλόν (è psilón), έψιλον).

second-person singular present active indicative of εἰμῐ́ (eimĭ́, to be)

second-person singular present active indicative of εἶμῐ (eîmĭ, to go)

Source: wiktionary.org