Why is it called pain "Chu"? Where does the word "Chu" come from and what does it mean?

This is what I transferred from someone else's blog, which is an explanation of thorns.

Spine is a commonly used word now, which originally refers to two kinds of plants: thorn and thorn.

Vitex negundo is a deciduous shrub of Verbenaceae. Also called Chu in ancient times, it was used for criminal struggle and flogging criminals. Therefore, Chu is also called "Jingchu", and those who are whipped are called "receiving Chu". Suffering from Chu is a painful thing, so the word "leaving" has the meaning of "pain", such as pain and suffering. Jing was also used to make women's hairpins in ancient times, which was called "Chai Jing". Later, it evolved into a modest name for his wife "Shi Jing" and "humble Jing", or simply "Jing".

Spines are deciduous shrubs of rhamnaceae. Its prickly branches are often used as fences by the people. The earliest prisoners were also surrounded by thorns. Later, "Cong Jing" became synonymous with prison. In the era of science, in order to prevent cheating in the examination room, the wall is also covered with thorns, so the examination room is also called "thorn yard" or "thorn enclosure". Thorns are often mixed with thorns in the wild, so the word "thorn" came into being. Thorns are the most likely to block roads, and they are also used to describe dangerous situations or chaotic situations, from which the idioms "through thorns" and "land of thorns" come.