污染 (wū rǎn) literally combines 污 (wū), meaning 'dirty' or 'filthy', and 染 (rǎn), meaning 'to stain' or 'to contaminate'. Together, they form the noun 'pollution' — the introduction of harmful substances or energy into the environment, degrading air, water, soil, or living systems. It is a neutral, formal term widely used in scientific, governmental, and media contexts.

The word commonly appears in compound nouns like 空气污染 (kōngqì wūrǎn, 'air pollution'), 水污染 (shuǐ wūrǎn, 'water pollution'), and 光污染 (guāng wūrǎn, 'light pollution'). It can also function as the object of verbs like 造成 (zàochéng, 'to cause'), 防止 (fángzhǐ, 'to prevent'), or 加剧 (jiājù, 'to worsen'). While it refers to environmental harm, it’s rarely used metaphorically (unlike English 'pollution' in phrases like 'pollution of ideas').