After using Google search, this is what I found:

[**dense**][1]
>/dɛns/

>adjective

>1.
**closely compacted in substance.**

>"as the storm cleared, a dense fog came down"
synonyms:	**thick**, heavy, opaque, soupy, murky, smoggy, impenetrable; More

>2.
informal
(of a person) stupid.

>"Am I being dense? I don't quite understand"

Definition (1) clearly states that 'dense' is synonymous with 'thick'.

[1]:https://www.google.com.hk/?hl=en&gws_rd=ssl#hl=en&q=dense+definition