Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
non-nullus (or written separately, non nullus, Verg. A. 11, 725), a, um, adj., some, several: non nullumst periculum, Plaut. Capt. 1, 1, 23; Ter. Ad. 2, 1, 68: esse nonnullo se Caesaris beneficio affectum, Caes. B. G. 7, 37, 4: nonnulla pars militum, id. B. C. 1, 13, 4: frumenti copiam nonnullam habere, id. ib. 1, 78, 1: non nulli amici, Cic. Mur. 20, 42: non nulla communia, id. Ac. 2, 22, 70: nonnullae cohortes, Caes. B. C. 1, 24.
Subst.: nonnulli, ōrum, m. (sc. milites), some, several, Caes. B. G. 1, 26.