lair (n.) Look up lair at Dictionary.com
Old English leger "bed, couch, grave; act or place of lying down," from Proto-Germanic *legraz (cognates: Old Norse legr "grave," also "nuptials" ("a lying down"); Old Frisian leger "situation," Old Saxon legar "bed," Middle Dutch legher "act or place of lying down," Dutch leger "bed, camp," Old High German legar "bed, a lying down," German Lager "bed, lair, camp, storehouse," Gothic ligrs "place of lying"), from PIE *legh- "to lie, lay" (see lie (v.2)). Meaning "animal's den" is from early 15c.