Dense
1 a: marked by compactness or crowding together of parts <dense vegetation> <dense traffic> b: having a high mass per unit volume <carbon dioxide is a dense gas>
2 a: slow to understand : stupid, thickheaded <was too dense to get the joke> b: extreme <dense ignorance>
3: having between any two elements at least one element <the set of rational numbers is dense>
4: demanding concentration to follow or comprehend <dense prose>
5: having high or relatively high opacity <a dense fog>