Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
sub-nĭger, gra, grum, adj., somewhat black, blackish: ventriosus, subniger, Plaut. Ps. 4, 7, 120: oculis, id. Merc. 3, 4, 55: labris (canum), Varr. R. R. 2, 9, 3: color (cutis), Cels. 5, 28, 4.