σύναρχος
From LSJ
τὸ ἐγδοχῖον τοῦ ὕδατος καὶ τὰ ἐν τῆι πόλει ὑδραγώγια → the water reservoir and the conduits in the city (or on the acropolis)
English (LSJ)
ὁ,
A partner in office, colleague, Arist.Pol.1287b31, IG5(1).124 (Laconia), 9(1).706 (Corc., iv B.C.), al., v.l. in D.C. 67.15.
German (Pape)
[Seite 1004] mitherrschend, Arist. pol. 3, 16.