vegetable, side dish, greens
菜 centers on edible plant matter, especially leafy greens and vegetables, and extends naturally to prepared vegetable dishes served alongside a main meal.
菜 combines the grass/plant radical 艹 with 采, which likely contributes the sound and originally depicted a hand picking from a tree, reinforcing the idea of harvesting edible plants.
The grass radical 艹 sits above 采, which looks like a hand picking from a tree. Picture gathering leafy greens from a plant: 菜 is a vegetable.
For サイ, imagine a sigh of satisfaction after eating a fresh side dish: sigh -> サイ, and the greens make you feel content.
vegetable
greens; vegetables
small dish (served as a part of an ordinary household meal); side dish
napa cabbage (Brassica rapa subsp. pekinensis); nappa cabbage; Chinese cabbage
edible wild plants
young greens; young herbs
coriander (Coriandrum sativum); cilantro; dhania; Chinese parsley
vegetable garden
rape blossoms; rapeseed flowers
vegetable diet
Japanese mustard spinach (Brassica rapa var. perviridis)
okara; soy pulp; tofu dregs; edible pulp separated from soybean milk in the production of tofu
hors d'oeuvre; appetizer; appetiser; starter
leaf mustard (Brassica juncea var. integrifolia); mustard greens
root vegetable
mizuna (Brassica rapa var. nipposinica); potherb mustard
Szechuan pickles; Sichuan vegetables; zha cai; pickled mustard plant stem
greens
rape (seed oil plant, Brassica campestris)
long chopsticks (for cooking, serving, etc.)