ἀμφοῖν (amphoin)
ἀμφοῖν is an Ancient Greek form of ἄμφω, meaning “both”. It is the genitive dual masculine adjective.
Found 587 times in the Ancient Greek texts on Socratos.
Where it is used
Thucydides, History of the Peloponnesian War 5.29.2: … ες, ἐν ἄλλοις τε καὶ ὅτι ἐν ταῖς σπονδαῖς ταῖς Ἀττικαῖς ἐγέγραπτο εὔορκον εἶναι προσθεῖναι καὶ ἀφελεῖν ὅτι ἂν ἀμφοῖν τοῖν πολέοιν δοκῇ, Λακεδαιμονίοις καὶ Ἀθηναίοις.
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.