CAI-4

('cai' in the fourth tone)

There are about 14 Chinese characters that are spoken 'cai'. The sound-determining element in about half of them is 采 = cai(3) = to pick. Another sound-determining element that occurs in several characters is 才 = cai(2) = ability.

菜 = vegetable, food

While the single-character can be used, it is usually better in spoken Chinese to use  the two-character words. 

青菜 = qing(1)cai(4) = vegetables, especially green vegetables

买菜 = mai(3) cai(4) = to buy groceries (not just vegetables)

我要去超市买菜. = Wo(3) yao(4) qu(4) chao(1)shi mai(3) cai(4) = I will go to the supermarket to buy groceries.

菜单 = cai(4)dan(1) = menu (both in restaurants and computer interfaces)

单 = dan(1) = single, alone; list of items on a paper