传染 (chuán rǎn) is a verb meaning 'to infect' or 'to be contagious.' It combines 传 (chuán), meaning 'to transmit' or 'to spread,' and 染 (rǎn), meaning 'to stain' or 'to become affected'—together evoking the idea of disease or pathogens spreading from one person or organism to another. The word emphasizes the process of transmission, not just the state of being infected.

This term is used primarily in medical, public health, and biological contexts—for example, when discussing viruses, bacteria, or other infectious agents. It commonly appears in passive constructions (e.g., 被传染) or as part of compound nouns like 传染病 (infectious disease). While it can occasionally describe non-biological contagion (e.g., emotions or behaviors), such usage is metaphorical and less frequent in everyday speech.