A cave or hollow place in the earth; usually applied to a cave, pit, or subterraneous recess, used for concealment, shelter, protection or security; as a lions den; a den of robbers or thieves. The beasts go into dens. The children of Israel made themselves dens. Job 37:8; Judges 6:2.

As a termination, in names of places, it denotes the place to be in a valley or near a wood.

To dwell as in a den.