Den (?), n. [AS. denn; perh. akin to G. tenne floor, thrashing floor, and to AS. denu valley.] 1. A small cavern or hollow place in the side of a hill, or among rocks; esp., a cave used by a wild beast for shelter or concealment; as, a lion's den; a den of robbers.
2. A squalid place of resort; a wretched dwelling place; a haunt; as, a den of vice. “Those squalid dens, which are the reproach of great capitals.” Addison.
3. Any snug or close retreat where one goes to be alone.
4. [AS. denu.] A narrow glen; a ravine; a dell. Shak.