Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
nāpus, i, m., a kind of turnip, a navew, Col. 2, 10, 23; 12, 56, 1; Plin. 18, 13, 35, § 131; 19, 5, 25, § 75; Mart. 13, 20 in lemm.