Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ambactus, i, m. [Celt. amb; Goth. andbahti = service; andbahts = servant], a vassal, a dependent upon a lord: ambactus apud Ennium linguā Gallicā servus appellatur. Paul. ex Fest. p. 4 Müll.: plurimos circum se ambactos clientesque habent, Caes. B. G. 6, 15; cf. Grimm, Gram. 2, p. 211; id. Antiq. p. 304.