Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
arcessītor, ōris, m. [arcesso], one that calls or fetches another (perh. only in the two foll. exs.): nemo arcessitor ex proximo, Plin. Ep. 5, 6, 45.
Hence, in judic. lang., an accuser, Amm. 29, 1, 44.