choy sum noun1 •A Chinese vegetable, a variety of Brassica rapa parachinensis subspecies, similar to bok choy but slimmer, with smooth green leaves and pale green stems, and clusters of flowers on the tips of the inner shoots.Added the chopped choy sum and stir it to release any excess water as steam. As the choy sum loses its water, add the chili and a good pinch of salt. — 2013
