From WordNet (r) 3.0 (2006) [wn]:
den
n 1: the habitation of wild animals [syn: lair, den]
2: a hiding place; usually a remote place used by outlaws [syn:
hideout, hideaway, den]
3: a unit of 8 to 10 cub scouts
4: a room that is comfortable and secluded
From The Collaborative International Dictionary of English v.0.48 [gcide]:
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.
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3. Any snug or close retreat where one goes to be alone.
[Colloq.]
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4. [AS. denu.] A narrow glen; a ravine; a dell. [Old Eng. &
Scotch] --Shak.
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From The Collaborative International Dictionary of English v.0.48 [gcide]:
Den \Den\, v. i.
To live in, or as in, a den.
[1913 Webster]
The sluggish salvages that den below. --G. Fletcher.
[1913 Webster]