Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
Bellocassi, ōrum (also Velocasses, ium, Caes. B. G 2, 4, and Velliocasses, Hirt. B. G. 8, 7), m., a people on the right bank of the Seine, from the mouth of the Oise to the town Le Pont de l’Arche, Caes. B. G. 7, 75