From The Collaborative International Dictionary of English v.0.48:
Dense \Dense\, a. [L. densus; akin to Gr. ? thick with hair or
leaves: cf. F. dense.]
1. Having the constituent parts massed or crowded together;
close; compact; thick; containing much matter in a small
space; heavy; opaque; as, a dense crowd; a dense forest; a
dense fog.
[1913 Webster]
All sorts of bodies, firm and fluid, dense and rare.
--Ray.
[1913 Webster]
To replace the cloudy barrier dense. --Cowper.
[1913 Webster]
2. Stupid; gross; crass; as, dense ignorance.
[1913 Webster]