Definitions of dense:

• adjective:   hard to pass through because of dense growth

  Example: "Dense vegetation"

• adjective:   permitting little if any light to pass through because of denseness of matter

  Example: "Dense smoke"

• adjective:   slow to learn or understand; lacking intellectual acuity

  Example: "So dense he never understands anything I say to him"

• adjective:   having high relative density or specific gravity

  Example: "Dense as lead"

• adjective:   closely crowded together

  Example: "A dense population"

• name:  A surname (very rare: popularity rank in the U.S.: #52201)