Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ălăternus, i, f. [perh. akin to Germ. Erle; Engl. alder], a shrub: Rhamnus Alaternus, Linn.; Col. 7, 6; Plin. 16, 26, 45, § 108.