The Sino-Japanese reading しん of 心 for the mental or spiritual side of a person. It is very common inside compounds and fixed expressions such as 心身 and 心・技・体; the ordinary standalone reading for 'heart/mind' is usually こころ.
innermost heart; true feelings; core of one's character
Focuses on what lies deep inside a person: their real feelings, nature, or character. In modern Japanese this しん reading is often encountered through compounds such as 本心.
Used for the physical or structural center of something. This meaning is normally written 芯 in everyday Japanese, especially for fruit cores, pencil leads, and the center of an object.
Refers to the anatomical heart, mainly as a technical or compound element in words such as 心拍 and 心音. The usual standalone everyday word for the organ is 心臓.
Archaic children's-language use meaning 'friend.' It is not used this way in modern everyday Japanese except when explaining old or childlike language.
