Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
pernĭo, ōnis, m. [perna], a kibe on the foot, a chilblain, Plin. 23, 3, 37, § 74; 23, 6, 58, § 109; 28, 16, 62, § 221.