Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
stagnĕus, a, um, v. stanneus.
stannĕus (stagnĕus), a, um, adj. [stannum], made of stannum: vasa, Plaut. Fragm. ap. Fest. s. v. narica, p. 166 Müll.; Plin. 30, 7, 19, § 38: cacabus, Col. 12, 42, 1: pyxis, Plin. 29, 2, 10, § 35; 30, 5, 12, § 38: nummi, Dig. 48, 10, 9.