A place where a wild animal lives, often underground and hidden, or a place where a person hides. (Cambridge Dictionary)
The resting or living place of a wild animal: Den. (Merriam – Webster)
A place where a wild animal lives. (Oxford Dictionaries)
A secret or private place in which a person seeks concealment or seclusion. (Oxford Dictionaries)
A lair is a place where a wild animal lives, usually a place which is underground or well-hidden. (Collins Dictionary)
Pirates Lair. Wikimedia Commons.
Entering the Tiger’s Lair.