Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
1. nĭgellus, a, um, adj. dim. [1. niger], somewhat black, dark (ante-class.): oculi suppaetuli nigellis pupulis, Varr. ap. Non. 456, 8: amiculum, id. ib. 550, 6: vina, Pall. 3, 25, 12: Cadmi nigellae filiae, i. e. the letters of the alphabet, Aus. Ep. 4, 74.