denn.[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.(Addison.)3. Any snug or close retreat where one goes to be alone.()[AS. denu.]4. A narrow glen; a ravine; a dell.(Shak.)v. i. To live in, or as in, a den.()The sluggish salvages that den below. (G. Fletcher.)