dense

adjective

1. permitting little if any light to pass through because of denseness of matter"dense smoke"
2. hard to pass through because of dense growth"dense vegetation"
3. having high relative density or specific gravity"dense as lead"
4. slow to learn or understand; lacking intellectual acuity"so dense he never understands anything I say to him"
5. having component parts closely crowded together"a compact shopping center"