late form for ἔστω, 3 sg. imper. of εἰμί (sum), IG 3.3509, BGU 419.13 (iii AD), etc.

1. as Substantive Verb, to be, to exist , οὐκ ἔσθ᾽ οὗτος ἀνήρ, οὐδ᾽ ἔσσεται (Odyssey by Homer); τεθνηῶτος, μηδ᾽ ἔτ᾽ ἐόντος (Odyssey by Homer); οὐκέτ᾽ ἔστι he is no more , (Euripides); θεοὶ αἰὲν ἐόντες (Iliad by Homer); ἐσσόμενοι posterity, (Iliad by Homer); ζώντων καὶ ὄντων Ἀθηναίων (Demosthenes Orator):—;so of cities, etc., ὄλωλεν, οὐδ᾽ ἔτ᾽ ἔστι Τροία (compare Troja fuit) , (Euripides)
2. of things, to be, exist , εἰ ἔστιν ἀληθέως [ ἡ τράπεζα] (Herdotus Historicus); ἕως ἂν ὁ πόλεμος ἦι so long as it last , (Thucydides)
3. to be , opp. to appearing to be , as esse to videri , τὸν ἐόντα λόγον the true story, (Herdotus Historicus); τὰ ὄντα ἀπαγγέλλειν (Thucydides); τῶι ὄντι, Lat. revera, in reality, in fact, (Plato Philosophus)
4. followed by the Relative, οὐκ ἔστιν ὅς, no one , (Iliad by Homer), etc.; εἰσὶν οἵ, Lat. sunt qui, (Thucydides), etc.; ἐστὶν ἅ some things , (Thucydides); also ἔστιν οἵ, for εἰσὶν οἵ, (Herdotus Historicus), etc.:—;so withrelat. Particles, ἔστιν ἔνθα, Lat. est ubi, (Xenophon Historicus), etc.; ἔστιν ὅπη, ἔσθ᾽ ὅπου, somewhere , or somehow , (Plato Philosophus), etc.; ἔστιν ὅπως in some manner , (Herdotus Historicus), etc.; ἔστιν ὅτε, ἔσθ᾽ ὅτε, sometimes , (Sophocles Tragicus), etc.
5. ἔστι impersonal, with infinitive, like πάρεστι, it is possible , (Homer), attic
6. to be , Copula connecting predicate with subject, both being in the same case, (Homer), etc.
7. sometimes εἶναι with Part. represents finite Verb, ἦν τεθνηκώς, for ἐτεθνήκει, (Aeschulus Tragicus); πεφυκός ἐστι = πέφυκε, (Aristophanes Comicus)
8. the Inf. is redundant in some phrases, ἑκὼν εἶναι (see. ἑκών II); τὸ ἐπ᾽ ἐκείνοις εἶναι quantum in illis esset , (Thucydides); τὸ σύμπαν εἶναι (Herdotus Historicus); τὸ νῦν εἶναι (Plato Philosophus), etc. (ML)