- 第二次 dì'èrcì the second timethe second time; second in a series
- 二次元 èrcìyuán two-dimensionalTwo-dimensional; having the dimensions of height and width
- 二次大战 èrcìdàzhàn World War IIThe Second World War; specifically the global conflict from 1939 to 1945. It is an abbreviation of [[第二次世界大战|第二次世界大戰|di4 er4 ci4 shi4 jie4 da4 zhan4]].
- 二次函数 èrcìhánshù quadratic functionA mathematical function where the highest power of the independent variable is two. is the second power
- 二次方 èrcìfāng squarethe product of a number multiplied by itself; a number to the second power
- 二次曲线 èrcìqūxiàn quadratic curvea curve of the second degree in geometry, including the circle, ellipse, hyperbola, and parabola; conic section
- 二次型 èrcìxíng quadratic form(mathematics) a quadratic form or a homogeneous polynomial of degree two (in many contexts also used to refer to quadrics)
- 二次曲面 èrcìqūmiàn quadric surfacea surface formed by a quadratic equation in three variables, such as a sphere, ellipsoid, or paraboloid; conicoid
- 二次曲 èrcìqū quadratic curvequadratic curve or conic section in geometry
- 二次根 èrcìgēn square rootnumber that, when multiplied by itself, produces a specified quantity
- 二次污染 èrcìwūrǎn secondary pollutionpollution caused by primary pollutants undergoing physical, chemical, or biological changes to form new harmful substances; also known as [[次生污染|次生汙染|ci4 sheng1 wu1 ran3]] or [[二次公害|二次公害|er4 ci4 gong1 hai4]]
- 二次能源 èrcìnéngyuán secondary energyEnergy source produced by processing or converting primary energy, such as electricity, gasoline, or coal gas
- 二次革命 èrcìgémìng Second RevolutionThe campaign in 1913 led by the Guomindang under [[孙中山|孫中山|sun1 zhong1 shan1]] against the rule of [[袁世凯|袁世凱|yuan2 shi4 kai3]] and the northern warlords.
- 第二次世界大战 dì'èrcìshìjièdàzhàn World War IIThe global conflict that lasted from 1939 to 1945 between the Allied and Axis powers
- 第二次汉字简化方案 dì'èrcìhànzìjiǎnhuàfāng'àn Second Chinese Character Simplification SchemeA set of simplified Chinese characters issued by the Chinese government in 1977 and later abolished in 1986.
- 第二次色 dì'èrcìsè secondary colora color produced by mixing two primary colors in equal proportions
- 二次世界大战 èrcìshìjièdàzhàn World War IIWorld War Two; the Second World War
- 二次公害 èrcìgōnghài secondary pollutionpollution resulting from the interaction of primary pollutants in the environment to form new harmful substances
- 二次多项式 èrcìduōxiàngshì quadratic polynomiala polynomial of the second degree
- 二次幂 èrcìmì squarea number multiplied by itself; the second power of a value
- 二次感染 èrcìgǎnrǎn secondary infectionA secondary infection occurring when a body already weakened by one pathogen is infected by another; specifically used in medical contexts.
- 二次方程 èrcìfāngchéng quadratic equation(math) quadratic equation
- 二次方程式 èrcìfāngchéngshì quadratic equationan equation in algebra where the highest power of the unknown variable is two