留心 (liú xīn) is a verb meaning 'to pay attention' or 'to be mindful of something.' Literally, 留 (liú) means 'to leave, to keep, or to retain,' and 心 (xīn) means 'heart' or 'mind.' Together, they evoke the image of 'keeping your mind on something'—holding your attention deliberately rather than letting it wander. It implies active, conscious focus, often with a sense of caution or care.

This word is commonly used in everyday spoken and written Chinese, especially when advising someone to notice details, avoid mistakes, or stay alert—for example, when giving directions, offering safety tips, or reminding students during learning. It’s slightly more formal and attentive than just 看 (kàn, 'to look') or 注意 (zhù yì, 'to pay attention'), carrying a gentle but earnest tone of vigilance and responsibility.