The natural meaning of Xiyan is as follows:

"Xiyan" is a rarely used famous saying. To take it a step further, it means not imposing political orders. What is "nature"? The word "nature" does not refer to the "nature" of natural science, but a term of philosophy, which can be interpreted as "that's how it is."

Source:

From Laozi's "Tao Te Ching·Chapter 23".

Original text:

I wish to express myself naturally. Therefore, the wind does not last forever, and the showers last all day. Who is this? world. Heaven and earth cannot last forever, how about humans? Therefore, those who practice Tao are the same as Tao; those who are virtuous are the same as virtue; those who lose are the same as loss. Those who are the same as Tao, Tao is also happy to gain it; those who are the same as virtue, virtue is also happy to gain it; those who are the same as loss, loss is also happy to gain it. If you don't believe it enough, you don't believe it.

Translation:

It goes without saying that it is natural for government orders to disturb the people as little as possible, so no matter how strong the wind is, it cannot blow for a whole morning, and no matter how strong the rainstorm is, it cannot last a whole day. Who created the storm? It is heaven and earth. Wind and rain cannot last forever, let alone people. Therefore, those who practice Tao are the same as Dao; those who are engaged in virtue are the same as virtue; those who are immoral and unethical will behave violently and wantonly.

Text interpretation:

So "Xiyan Nature" does not mean "rarely talks about the theories of natural science", it means governing things, formulating laws and regulations, Let nature take its course. It is natural for a ruler to give fewer orders. In this chapter, Laozi discusses the significance of rulers giving less orders and illustrates the problem through changes in nature.