愣住 (lèng zhù) is a verb meaning 'to freeze up' or 'to be visibly stunned' — describing the physical and mental pause that occurs when someone is suddenly shocked, surprised, or overwhelmed. The first character 愣 (lèng) means 'dazed' or 'stunned', carrying a sense of mental blankness; the second character 住 (zhù) functions as a resultative complement indicating 'to stop' or 'to halt in place'. Together, they vividly convey an involuntary, momentary cessation of movement and speech — often accompanied by widened eyes, open mouth, or rigid posture.

This expression is commonly used in spoken and written Chinese to depict immediate, visceral reactions: to unexpected news, sudden danger, awkward social moments, or emotionally charged encounters. It emphasizes outward perceptibility — others can *see* the person has frozen — distinguishing it from internal states like confusion or doubt. While neutral in register, it’s more common in informal or narrative contexts than formal reports or academic writing.