乙炔 (yǐ quē) is the Chinese term for acetylene, a colorless, highly flammable hydrocarbon gas with the chemical formula C₂H₂. It is widely used in industrial applications, especially in oxy-acetylene welding and cutting of metals due to its extremely high flame temperature (over 3,300°C when burned with oxygen). The character 乙 (yǐ) is the second of the ten Heavenly Stems, historically used in naming organic compounds in Chinese chemical nomenclature; 炔 (quē) specifically denotes alkynes — hydrocarbons containing a carbon–carbon triple bond. Together, 乙炔 literally signals 'the alkyne derived from ethane', following systematic IUPAC-based naming conventions adopted in Chinese scientific terminology.

This word appears almost exclusively in technical, scientific, or safety-related contexts — such as chemistry textbooks, industrial manuals, laboratory safety briefings, or occupational health guidelines. Learners will rarely encounter it in daily conversation but may see it on warning labels, chemical inventories, or vocational training materials. Pronunciation must preserve both tones: yǐ (third tone) and quē (first tone); mispronouncing quē as què (fourth tone) can cause confusion with unrelated words like 缺 (to lack).