Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
2. sōnus, a, um, adj. [sono], sounding, resounding, Isid. Orig. 1, 4, 4.
3. Sōnus, i, m., = Σῶνος, a river of India, a branch of the Ganges, Plin. 6, 18, 22, § 65.