γνώμων
gnōmōn

pin of a sundial

Δι’ ἣν αἰτίαν καὶ τὰ μεγέθη τῶν ἡμερῶν ἴσα ἐστὶν ἐν Διδύμοις καὶ ἐν Καρκίνῳ, καὶ ἐν τοῖς ὡροσκοπίοις αἱ ὑπὸ τῶν γνωμόνων γραφόμεναι γραμμαὶ ἴσον ἀπέχουσι τοῦ θερίνου τροπικοῦ καὶ ἐν Καρκίνῳ καὶ ἐν Διδύμοις· ἐξ ἴσου γὰρ κεῖται πρὸς τὸ θερινὸν σημεῖον τὰ δύο δωδεκατημόρια.

‘For this reason the lengths of the days are equal in Gemini and in Cancer, and also on the sundials the lines described by the gnomons are equally far from the summer tropic both in Cancer and in Gemini: for the two ‘twelfth parts’ lie in an equal way in relation to the summer point.’

Πρόδηλον δὲ τοῦτο καὶ ἐκ τῶν σκιοθήρων· τὸ γὰρ ἄκρον τῆς τοῦ γνώμονος σκιᾶς σχεδὸν ἐφ’ ἡμέρας μ ἐπιμένει ταῖς τροπικαῖς γραμμαῖς.

‘And this is evident from the sundials too: for the tip of the gnomon’s shadow stays on the tropical lines for approximately 40 days.’

used as a 'pars pro toto', rare

Πᾶσαν οὖν τὴν ἀλήθει[αν] ἡμῖν ἐξετίθι καὶ ἐπ[ὶ το]ῦ ἔργου ἐδίκνυον ἐ[κ το]ῦ ὅλμου τοῦ λιθίνου [ὃς ἐκ]αλεῖτο Ἑλληνιστὶ [γν]ώμων.

‘He then expounded to us the whole truth and showed it in practice from the stone cylinder, which was called “gnomon” in Greek.’