The word 出卖 is formed by combining two characters whose core meanings create a vivid conceptual metaphor. The first character, 出 (chū), fundamentally means "to go out" or "to extend outward". The second, 卖 (mài), means "to sell". Together, they paint the picture of taking something that is typically internal, private, or entrusted, like secrets, loyalty, or principles, and actively offering it outwardly to an external party in a transactional manner, thus giving rise to its primary meaning of "to betray" or "to sell out".