Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
dŭālis, e, adj. [duo], that contains two: numerus (nasi), i. e. the dual number, duality, Lact. Opif. D. 10, 9.
In gram. lang.: numerus, the dual, Quint. 1, 5, 42 al.