dense in WordNet English dictionary

1. having high relative density or specific gravity
   "dense as lead"
   dense 
   
2. hard to pass through because of dense growth
   "dense vegetation"; "thick woods"
   dense  thick 
   
3. slow to learn or understand; lacking intellectual acuity
   "so dense he never understands anything I say to him"; "never met anyone quite so dim"; "although dull at classical learning, at mathematics he was uncommonly quick"- Thackeray; "dumb officials make some really dumb decisions"; "he was either normally stupid or being deliberately obtuse"; "worked with the slow students"
   dense  dim  dull  dumb  obtuse  slow 
   
4. permitting little if any light to pass through because of denseness of matter
   "dense smoke"; "heavy fog"; "impenetrable gloom"
   dense  heavy  impenetrable