What do grass and green horses have in common?

 ANSWER: They can both mean "starch" (풀, 녹말).

Actually, 풀 can mean either "grass," "paste," "starch," or "glue," and the 말 in 녹말 (綠末) means "powder," not "horse." I was just being silly.

녹말 (綠末) is a Sino-Korean word that means "starch," and 풀 is the pure Korean word for "starch." An article HERE says that 녹말 comes from 녹두분말 (綠豆粉末), which literally means "green (綠) bean (豆) powder (粉末)." 녹두 (綠豆) refers to "mung beans," which supposedly contain a lot of starch.

Another Sino-Korean word that means "starch" is 전분 (澱粉), which literally means "dreg (澱) powder (粉)," or "the powder of dregs."