呻吟 (shēn yín) is a verb meaning 'to moan' or 'to groan'—a low, involuntary sound expressing physical pain, discomfort, or intense emotion such as sorrow or frustration. The character 呻 (shēn) originally refers to a soft, drawn-out vocalization, often associated with breathing or distress; 吟 (yín) means 'to chant' or 'to hum', implying a sustained, melodic, or plaintive tone. Together, they form a reduplicative compound emphasizing the repetitive, rhythmic quality of the sound.

This word is commonly used in medical, literary, or empathetic contexts—e.g., describing someone in pain, an injured animal, or even metaphorically for a struggling system ('the old bridge seemed to 呻吟 under the weight'). It carries a slightly literary or solemn register and is rarely used humorously or casually. Unlike casual interjections like 'ouch', 呻吟 implies deeper or prolonged suffering and is seldom used for minor annoyances.