Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
1. strūma, ae, f. [struo], a scrofulous tumor, struma, Cels. 5, 28, 7; 1, 9 fin.; Plin. 8, 51, 77, § 206; 22, 14, 16, § 38; 26, 5, 14, § 26 al.: qui exsecant pestem aliquam, tamquam strumam civitatis, Cic. Sest. 65, 135; cf. sarcastically: Vatinii strumam sacerdotii διβάφῳ vestiant, id. Att. 2, 9, 2.
strūmus, i, m. [1. struma], a plant that cures the struma, called also strychnos and cuculus, Plin. 27, 8, 44, § 68; App. Herb. 74.