Neuter plural(s). The Homeric (Odyssey 24.208) headword is taken to refer to shepherds' huts: "and all about it ran the sheds in which ate, and sat, and slept the servants that were bondsmen".
The definition appearing here originates in Moeris' Attic Lexicon ("klisi/a are where couples stay", repeated in the Etymologicum Gudianum and Etymologicum Magnum), and especially Porphyrius, Quaestionum Homericarum ad Odysseam pertinentium reliquiae ad loc.: after defining kli/sion as comparable to klisi/a (kappa 1811, kappa 1812), Porphyrius goes on: "The place containing many beds and seats was called a kli/sion, in the same way we call it koitw/n [bed-chamber, from kei=mai 'lie down'], Attic calls [our koitw/n] a dwma/tion 'room, bedroom', and Homer a qa/lamos 'chamber'." At the end of his extensive scholion, trying to work out what the word means, Porphyrius still situates the kli/sion outside the house.
The gloss is derived from Latin cubiculum (see Lampe s.v.).