The Chinese word 背心 (bèixīn), meaning "vest" or "sleeveless garment", is a compound formed through semantic combination. It literally translates to "back-heart", where 背 (bèi) means "back" and 心 (xīn) means "heart" or "center". This construction vividly describes the garment's primary function: it covers the core torso, the back and the chest (over the heart), while notably leaving the arms uncovered. The term is therefore a metaphorical, descriptive compound that highlights the item's essential coverage area, distinguishing it from full-sleeved tops or jackets.