#ExtremelyCloseFriendBosomFriend

知己 (zhījǐ) Extremely close friend/ Bosom friend 

The character “知 (zhī)” means to know and “己 (jǐ)” means self.

Example:

Yī gè rén huì yǒu hěnduō péngyou, dàn nénggòu chéngwéi zhījǐ de què hěn shǎo. 一个人会有很多朋友，但能够成为知己的却很少。

A person will have many friends, but just a …