The Collaborative International Dictionary of English v.0.48:

Pyjama \Py*ja"ma\, n. [Hind. p[=a]e-j[=a]ma, literally, leg
   clothing.]
   In India and Persia, thin loose trowsers or drawers; in
   Europe and America, drawers worn at night, or a kind of
   nightdress with legs. Usually used in the plural. See
   pajamas. [Written also paijama pajama.] [Chiefly
   British variant of pajama.]
   [1913 Webster +PJC] Pyjamas

WordNet (r) 3.0 (2006):

pajama
    n 1: a pair of loose trousers tied by a drawstring around the
         waist; worn by men and women in some Asian countries [syn:
         pajama, pyjama]
    2: (usually plural) loose-fitting nightclothes worn for sleeping
       or lounging; have a jacket top and trousers [syn: pajama,
       pyjama, pj's, jammies]