Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† ăthēra, ae, f., = ἀθήρα, a medicine prepared from arinca: Olyram arincam diximus vocari. Hac decoctā fit medicamentum, quod Aegyptii atheram vocant, Plin. 22, 25, 57, § 121.