The Collaborative International Dictionary of English v.0.48:

nightclothes \nightclothes\ n.
   garments designed to be worn in bed, such as pyjamas, a
   nightgown, etc.

   Syn: nightwear.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Pajamas \Pa*ja"mas\, n. pl. [Hind. p[=a]-j[=a]ma, p[=a]ej[=a]ma,
   lit., leg closing.]
   Originally, in India, loose drawers or trousers, such as
   those worn, tied about the waist, by Mohammedan men and
   women; by extension, a similar garment adopted among
   Europeans, Americans, etc., for wear in the dressing room and
   during sleep; also, a suit consisting of drawers and a loose
   upper garment for such wear. [Also spelled pyjamas.]
   [Webster 1913 Suppl.]

The Collaborative International Dictionary of English v.0.48:

Pyjamas \Py*ja"mas\, or, chiefly U. S., Pajamas \Pa*ja"mas\, n.
   pl.
   A garment, similar to the Oriental pyjama (which see),
   adopted among Europeans, Americans, and other Occidentals,
   for wear in the dressing room and during sleep; also, a suit
   of drawers and blouse for such wear.
   [Webster 1913 Suppl.]