den

A small cavern or hollow place in the side of a hill, or among rocks; especially, a cave used by a wild animal for shelter or concealment.

a den of robbers

Daniel was put into the lions’ den.

A squalid or wretched place; a haunt.

a den of vice

an opium den; a gambling den

A comfortable room not used for formal entertaining.

Near-synonyms: family room, sunroom, Florida room, Arizona room, rec room, playroom

Synonym of fort (“structure improvised from furniture, etc. for playing games.”).

Our little girls love using bedsheets and other stuff around the house to make dens in the living room and pretending they're on adventures.

A narrow glen; a ravine; a dell.

I have made several visits of late to the Den of Rubislaw

To ensconce or hide oneself in (or as in) a den.

Of an animal, to use as a den; to take up residence in.

Although present in virtually all habitats, it preferred to den in caves, so its distribution, especially in cold, northern areas, may have been limited to limestone and other rocky regions where caves form.

“Denning” – behaviour around making dens – has changed and bears are swimming long distances, but, says Aars, there is still enough sea ice in the spring for the bears to hunt successfully.

Abbreviation of denier (a unit of weight).