Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
2. Ănĭēnus, a, um, adj. [Anio], of or pertaining to the Anio: fluenta, Verg. G. 4, 369: unda, Prop. 1, 20, 8: lympha, id. 4, 15, 4.