Dictionary:

bok choy

  (bŏk' choi')

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bok choy

Brassica rapa subsp. chinensis ( School Division, Houghton Mifflin Company)

A Chinese vegetable (Brassica rapa subsp. chinensis) in the mustard family, having a loose head of dark green leaves with thick white stems. Also called celery cabbage, Chinese cabbage.

[Chinese (Cantonese) paāk ts'oì, equivalent to Chinese (Mandarin) báicài : bái, white + cài, vegetable.]

[bahk CHOY] Also called Chinese white cabbage, pak choy, pak choi and white mustard cabbage, bok choy is a mild, versatile vegetable with crunchy white stalks and tender, dark green leaves. It resembles a bunch of wide-stalked celery with long, full leaves. Choose bunches with firm, white stalks topped with crisp, green leaves. Bok choy is available year-round in most supermarkets and should be refrigerated airtight for no more than 3 to 4 days. It can be used raw in salads, in a stir-fry or as a cooked vegetable. Bok choy is related to but not the same as chinese cabbage.

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The noun has 2 meanings:

Meaning #1: Asiatic plant grown for its cluster of edible white stalks with dark green leaves
  Synonyms: bok choi, pakchoi, Chinese white cabbage, Brassica rapa chinensis

Meaning #2: elongated head of dark green leaves on thick white stalks
  Synonym: bok choi