Answer: Out.
Each character for "Sui" minus one character for "Xi" is the character for "山", and the character for "Sui" is the "reunion of two mountains".
Out, a commonly used Chinese character (first-level character), pronounced as chū, was first seen in oracle bone inscriptions. Its original meaning is from the inside to the outside, and it can also be extended to leave, send out, take out, hand over, pay out, produce. , produce, appear, reveal and other meanings.
Interpretation of ancient books
Shuowenjiezi
Progress. Like the bark of a tree, it nourishes and reaches its peak. Everything that comes out comes from out. Rule cut.
Shuowenjiezizi
(Out) Enter.
Originally called 艸木. It is extended to the meaning of growth. Also, it is said that going out is the opposite of entering in.
Importantly, the tree is like a tree.
Hereby are the authors of this article. Jinzheng. Nowadays, it is also beneficial to the people. The wood grows from the talent. It's getting bigger day by day. Rule cut. Fifteen parts. Everything that comes out comes from coming out.