Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† thallus, i, m., = θαλλός, a green stalk, green bough: cepae, Col. 11, 3, 58; Pall. Febr. 24, 4: Amyclaeus, perh. a myrtlebough, Verg. Cir. 376; Vulg. 2 Macc. 14, 4.