An idiom with more than four characters to describe the deep friendship between "friends": sworn knot, hate to know each other late, like each other, sworn friends, brothers and sisters, good friends, life and death acquaintance, talk about everything, never talk about anything. Between you and me, our friendship is deep, our love is as deep as the sea, we are friends in times of need, our brothers and sisters are as strong as the mountains and rivers.

Yì jié jīn lán: yì jié jīn lán

[Definition] Make friends who are very agreeable.

[Source] "Taiping Yulan" quotes "Wu Lu": "Zhang Wen is a talented person; he pays homage to the general; he betroths Shu and Zhuge Liang to form a sworn alliance with Jin Lan."

hate xiangzhiwan: hèn xiāng zhī wǎn

[Definition] hate: regret; xiangzhi: understand each other and have deep feelings. Regret that it was too late to form a friendship with each other. Describes new friendships and deep feelings.

[Source] "Historical Records·Biography of Wei Qiwu Anhou": "The two of them are attracted to each other, and they travel like a father and son. They enjoy each other so much that they never tire of each other, and they hate that they know each other too late."

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Love and harmony: qíng tóu yì hé

[Explanation] Tou: to be in harmony. Describes that the two parties are harmonious in their thoughts and feelings and get along well.

[Source] "Journey to the West" by Wu Cheng'en of the Ming Dynasty: "The Yuanzi of Nazhen and the traveler became brothers; the two fell in love with each other and would never let go." ?

Inseparable friends ：mò nì zhī jiāo

[Explanation] Mo Ni: no conflict, harmonious feelings; Jiao: communication, friendship. Refers to a very good friend.

[Source] "Zhuangzi: The Great Master": "The three of them looked at each other and smiled; they never went against their will; so they became friends."

Similar brotherhood: qíng tóng shǒu zú

[Interpretation] Siblings: a metaphor for brothers. The friendship is very deep, like brothers.

[Source] Tang Dynasty Li Hua's "Diao Ancient Battle Text": "Who doesn't have brothers, they are like feet and hands."

Love is as deep as the sea: qíng shēn sì hǎi

[Definition] Describes love as deep and immeasurable as the sea.

[Source] "The Romance of the West Chamber" by Cui Shipei of the Ming Dynasty: "The spring boredom is so hard to bear, after all, love is as deep as the sea."