WordNet sense 1 ((botany) of leaf shapes; of leaves having no divisions or subdivisions):

unsubdivided

WordNet sense 2 (lacking in insight or discernment):

purblind

WordNet sense 3 (lacking discernment):

undiscerning

WordNet sense 4 (slow to learn or understand; lacking intellectual acuity):

dense, dim, dull, dumb, slow

WordNet sense 5 (lacking or marked by lack of intellectual acuity):

stupid