Sense

1. (with personal accusative and infinitive) it behoves one to, it is necessary to, one must
2. (with impersonal accusative and infinitive)
3. (when used in absolute an infinitive may be supplied)

Examples

• λάλησον πρὸσ τοὺσ υἱοὺσ Ἰσραήλ, λέγων. ψυχὴ ἐὰν ἁμάρτῃ ἔναντι Κυρίου ἀκουσίωσ ἀπὸ πάντων τῶν προσταγμάτων Κυρίου, ὧν οὐ δεῖ ποιεῖν, καὶ ποιήσει ἕν τι ἀπ̓ αὐτῶν. (Septuagint, Liber Leviticus 4:2)
• Καὶ ἡ ψυχὴ ἣ ἂν ἁμάρτῃ καὶ ποιήσῃ μίαν ἀπὸ πασῶν τῶν ἐντολῶν Κυρίου, ὧν οὐ δεῖ ποιεῖν, καὶ οὐκ ἔγνω, καὶ πλημμελήσῃ καὶ λάβῃ τὴν ἁμαρτίαν, (Septuagint, Liber Leviticus 5:17)
• καὶ εἶπε Βοόζ. ἐν ἡμέρᾳ τοῦ κτήσασθαί σε τὸν ἀγρὸν ἐκ χειρὸσ Νωεμὶν καὶ παρὰ Ροὺθ τῆσ Μωαβίτιδοσ γυναικὸσ τοῦ τεθνηκότοσ, καὶ αὐτὴν κτήσασθαί σε δεῖ ὥστε ἀναστῆσαι τὸ ὄνομα τοῦ τεθνηκότοσ ἐπὶ τῆσ κληρονομίασ αὐτοῦ. (Septuagint, Liber Ruth 4:5)
• καὶ εἶπεν αὐτῷ. εἰπὸν δὴ πρὸσ αὐτήν. ἰδοὺ ἐξέστησασ ἡμῖν πᾶσαν τὴν ἔκστασιν ταύτην. τί δεῖ ποιῆσαί σοι̣ εἰ ἔστι λόγοσ σοι πρὸσ τὸν βασιλέα ἢ πρὸσ τὸν ἄρχοντα τῆσ δυνάμεωσ̣ ἡ δὲ εἶπεν. ἐν μέσῳ τοῦ λαοῦ ἐγώ εἰμι οἰκῶ. (Septuagint, Liber II Regum 4:13)
• καὶ εἶπε πρὸσ Γιεζί. τί δεῖ ποιῆσαι αὐτῇ̣ καὶ εἶπε Γιεζὶ τὸ παιδάριον αὐτοῦ. καὶ μάλα υἱὸσ οὐκ ἔστιν αὐτῇ, καὶ ὁ ἀνὴρ αὐτῆσ πρεσβύτησ. (Septuagint, Liber II Regum 4:14)

Source: Ancient Greek entries from Wiktionary