Definition of denned:
(n) :
A comfortable room not used for formal entertaining.
(n) :
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.
(n) :
A squalid or wretched place; a haunt.
(n) :
A group of Cub Scouts of the same age who work on projects together.
(n) :
Synonym of fort (“structure improvised from furniture, etc. for playing games.”).
(v) :
(intransitive, zoology) Of an animal, to use as a den; to take up residence in.