Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
arcārĭus, a, um, adj. [arca, I. B.], of or pertaining to a money-box or ready money: nomina, Gai. Inst. 1. 3, § 131 Goes.
Hence, arcārĭus, i, m., a treasurer (late Lat.): arcarii gazae tuae, Vulg. Esth. 3, 9: arcarius civitatis, ib. Rom. 16, 23; Dig. 40, 5, 41.
Also, a controller of public revenues, Lampr. Alex. Sev. 43.