Den \Den\ (d[e^]n), 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. [1913 Webster] 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. [1913 Webster] 3. Any snug or close retreat where one goes to be alone. [Colloq.] [1913 Webster] 4. [AS. denu.] A narrow glen; a ravine; a dell. [Old Eng. & Scotch] --Shak. [1913 Webster]