'Jū xīn' literally combines 'jū' (to dwell, reside) and 'xīn' (heart, mind), suggesting where one’s intention or motive 'resides' — that is, one’s underlying purpose or inner motive. It carries strong connotative weight and is rarely neutral; in modern usage, it almost always implies hidden, often morally questionable or malicious intent.

This term appears frequently in formal writing, legal contexts, and moral criticism — for example, when accusing someone of ulterior motives behind seemingly kind actions. It is not used for innocent or everyday intentions (for which you’d use 意图 yìtú or 用心 yòngxīn); rather, 居心 signals suspicion, judgment, or condemnation. The word functions as a noun and typically appears after verbs like '有' (to have), '叵测' (unfathomable), or '不良' (bad), reinforcing its evaluative nature.