ἕλεσι (helesi)
ἕλεσι is an Ancient Greek form of ἕλος, meaning “marsh”. It is the dative plural neuter noun.
Found 27 times in the Ancient Greek texts on Socratos.
Where it is used
Thucydides, History of the Peloponnesian War 1.110.2: Αἴγυπτος δὲ πάλιν ὑπὸ βασιλέα ἐγένετο πλὴν Ἀμυρταίου τοῦ ἐν τοῖς ἕλεσι βασιλέως· τοῦτον δὲ διὰ μέγεθός τε τοῦ ἕλους οὐκ ἐδύναντο ἑλεῖν, καὶ ἅμα μαχιμώτατοί εἰσι τῶν Αἰγυπτίων οἱ ἕλειοι.
All forms of ἕλος (declension table)
Source: Socratos (socratos.org), a free reader for Ancient Greek and Latin. Grammar from the Perseus Treebank and Morpheus; dictionary entries from Liddell-Scott-Jones, A Greek-English Lexicon (Perseus Digital Library, CC BY-SA). Counts are from the texts on Socratos.