知音

Etymology
From the old Chinese story about the deep friendship between two men, (a qin player) and  (a woodcutter). Despite Ziqi's humble background, upon hearing Boya play his qin he was surprisingly able to tell which subjects each of the pieces represented.

Noun

 * 1) friend keenly appreciative of one's talents; bosom friend; intimate friend; soul mate

Verb

 * 1)  to have a thorough understanding of music; to be proficient in music