A lair of wild beasts (Psalm 10:9; 104:22; Job 37:8); the hole of a venomous reptile (Isaiah 11:8); a recess for secrecy "in dens and caves of the earth" (Hebrews 11:38); a resort of thieves (Matthew 21:13; Mark 11:17). Daniel was cast into "the den of lions" (Dan. 6:16, 17). Some recent discoveries among the ruins of Babylon have brought to light the fact that the practice of punishing offenders against the law by throwing them into a den of lions was common.

Noah Webster's New International Dictionary of the English Language

1. (n.) 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. (n.) A squalid place of resort; a wretched dwelling place; a haunt; as, a den of vice.

3. (n.) Any snug or close retreat where one goes to be alone.

4. (n.) A narrow glen; a ravine; a dell.

5. (v. i.) To live in, or as in, a den.