The word 脾气 is formed through a conceptual fusion rooted in traditional Chinese medicine and philosophy. It combines 脾 (pí), meaning "spleen", an organ traditionally believed to influence one's vitality and digestion, with 气 (qì), meaning "energy", "air", or "vital force". The concept arises from the ancient belief that the condition of one's spleen and the flow of its associated qi directly influenced a person's disposition and emotional state. Thus, the term metaphorically extends the idea of a physical, internal energy from an organ to describe a person's inherent temperament or mood, framing one's nature as a kind of foundational, somatic energy.