The Collaborative International Dictionary of English v.0.48:

Lair \Lair\ (l[^a]r), n. [OE. leir, AS. leger; akin to D. leger,
   G. lager couch, lair, OHG. legar, Goth. ligrs, and to E. lie.
   See Lie to be prostrate, and cf. Layer, Leaguer.]
   [1913 Webster]
   1. A place in which to lie or rest; especially, the bed or
      couch of a wild beast.
      [1913 Webster]

   2. A burying place. [Scot.] --Jamieson.
      [1913 Webster]

   3. A pasture; sometimes, food. [Obs.] --Spenser.
      [1913 Webster]

WordNet (r) 3.0 (2006):

lair
    n 1: the habitation of wild animals [syn: lair, den]

Moby Thesaurus II by Grady Ward, 1.0:

76 Moby Thesaurus words for "lair":
   abri, adytum, antre, ashram, asylum, bolt-hole, bordello, brothel,
   bunker, burrow, cache, cathouse, cave, cavern, cell, clip joint,
   cloister, concealment, corner, couch, cove, cover, covert,
   coverture, cranny, cubby, cubbyhole, dark corner, den,
   den of thieves, dive, dugout, dump, earth, fleshpots, form,
   foxhole, funk hole, grot, grotto, gyp joint, hermitage, hideaway,
   hideout, hidey hole, hiding, hiding place, hole, hollow,
   holy of holies, ivory tower, joint, lodge, mew, nest, niche, nook,
   privacy, recess, refuge, retreat, run, sanctuary, sanctum,
   sanctum sanctorum, secret place, sewer, sporting house, stash,
   stews, subterrane, subway, tunnel, undercovert, warren,
   whorehouse