The Collaborative International Dictionary of English v.0.48:

pe-tsai \pe-tsai\ n.
   A plant with an elongated celerylike head of broadstalked
   leaves used as a vegetable in east Asia.

   Syn: Chinese cabbage, celery cabbage, napa, Brassica rapa
        pekinensis.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

pe-tsai
    n 1: plant with an elongated head of broad stalked leaves
         resembling celery; used as a vegetable in east Asia [syn:
         Chinese cabbage, celery cabbage, napa, pe-tsai,
         Brassica rapa pekinensis]