The Collaborative International Dictionary of English v.0.48:

hideout \hide"out\ (h[imac]d"out), n.
   a hiding place; usually a remote place used by outlaws.

   Syn: hideaway, den.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

hideout
    n 1: a hiding place; usually a remote place used by outlaws
         [syn: hideout, hideaway, den]

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "hideout":
   adytum, ashram, asylum, bolt-hole, cache, cell, cloister,
   concealment, corner, cover, covert, coverture, cranny, cubby,
   cubbyhole, dark corner, den, dugout, foxhole, funk hole, haven,
   hermitage, hideaway, hidey hole, hiding, hiding place, hole,
   holy of holies, ivory tower, lair, mew, niche, nook, privacy,
   recess, refuge, retreat, rock pile, sanctuary, sanctum,
   sanctum sanctorum, secret place, shelter, stash, undercovert