Lewis & Short

adversĭtor (archaic advor-), ōris, m. [adversus], one who goes to meet another; a slave who went to meet his master, in order to conduct him home:advorsum ierant proprie locutus est, nam adversitores dicuntur,” Don. ad Ter. Ad. 1, 1, 1; cf. also Plaut. Most. 4, 1, 23, and 2, 32. Among the dramatis personæ of the Mostellaria of Plautus, PHANISCVS ADVORSITOR is found; but the word is nowhere used in the play itself.