Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
trĕbax, ācis, adj. [contr. from the Gr. τριβακός], practised, skilled in the ways of the world, cunning, crafty (lat. Lat.): trebacissimus senex, Sid. Ep. 1, 11 med.
Adv.: trĕbācĭter, cunningly, slyly, Sid. Ep. 9, 11 med.